I don't think you can find the kind of hotel you are looking for in Bologna, especially in that price range. You can find atmospheric b&bs in palazzi, but Bologna can be about expensive as Milan or Paris when it comes to nice hotels. Add to that it is fairly frigid in Bologna come December. There are porticoes that cover the streets, and that is a real plus if it is raining, plus the hearty food. However, those same stone portici also act as refrigerators and wind-tunnels, and the sun doesn't reach you. So it is a mixed bag.

Naples is much more budget friendly for splashing out (so long as you avoid Christmas) and you can luck out with some really pleasant dry weather. If you have any interest in seeing Pompei, it can be ideal weather for pounding those stones. If you love art, the Capodimonte museum to me rivals the Louvre for great-art-in-a-great-palace, all the more fun for not being renovated to a fare-the-well. If it is raining, you can spend hours there as well as Naples' unrivaled Archeological Museum -- which has breathtaking mosaics from Pompei and classical statues from Rome.

If you get a brilliant day in Naples, and want to get up real early, you can take a train to Salerno and then bus all along the Amalfi coast, stopping for lunch. Or you can go to Paestum. If the seas are glass, you can take a boat to Capri (where it might be much colder I would think.) Or boat to Ischia and take in a real bubbling hot spring instead of a Jacuzzi. (I've never been.)

Can't really compare with Sevilla, which I have never been to in December. Obviously there is quite a difference in food and ambience. If you were thinking something very peaceful for your weekend, Naples is not that.

http://www.letsbookhotel.com/en/italy/napoli/hotels-accommodation/fac/jacuzzi.aspx

If a hotel advertises a rooftop hot tub, it is unlikely to be open in December. You should double check all reviews with recent ones on booking.com and Tripadvisor.

I know I am stretching it with the jacuzzi, though even a bathtub that makes bubbles could do (like the junior suite at the 4 Viale Masini Design Hotel in Bologne - though it is next to the train station and I'm not sure that's the nicest area). I had read that, although cold, there are very often blue skies in Bologne in December. I am Canadian, so the cold doesn't bother me too much (though my husband....). I will consider the Naples possibility too.

(And I am willing to forgo a tub if the hotel is nice enough. Was looking at I Portici Hotel Bologna or il convento dei fiori di seta). In Naples, a junior suite at La Ciliegina Lifestyle Hotel looks nice too. I admit I am just afraid of finding Naples too loud and dirty with not as much to do (day trips included) as Bologne? Not afraid of the crime and all that. Very interesting in eating great Italian food!

I love Sevilla - the undisputed queen of all the cities in Andalucía with its rich Roman, Christian, Jewish, Moslem, Gitano history and culture. You could easily make a over the top romantic weekend here.

I guess you'll have to pay some 100€/night for a nice hotel with jacuzzi in December. Here are some Sevilla hotels with jacuzzi: http://www.tvtrip.es/cihCVSL_aw-sevilla-hoteles-jacuzzi

Can recommend the Arab bath-house Aire de Sevilla. A friend of mine went five times in a week...: http://www.airedesevilla.com/

Experience real deal flamenco in intimate Casa de la Memória in the midst of the beautiful Santa Cruz district. Popular with tourists, but only great artists perform here. Perfect intro to this art so characteristic of Andalucía and Sevilla: http://www.tripadvisor.com/Attraction_Review-g187443-d539294-Reviews-Casa_de_la_Memoria_de_Al_Andalus-Seville_Province_of_Seville_Andalucia.html

Lots of fabulous small tapas bars and restaurants. Azahar lives in Sevilla, and has got tons of great suggestions, she knows what she talks about: http://azahar-sevilla.com/sevilletapas/

Two of my favourites:
Eslava: http://azahar-sevilla.com/sevilletapas/category/eslava/
Enrique Becerra: http://azahar-sevilla.com/sevilletapas/category/enrique-becerra/

Two informative sites about Sevilla:
To the point: http://www.andalucia.com/cities/sevilla.htm
More detailed: http://www.exploreseville.com/index.htm

And my home town Oslo in December can be very nice, only some eight hours light pr. day, but the Christmas preparation atmosphere is at the same time both hectic/festive and very relaxing. But expensive...

Naples is very loud and mostly very dirty, but the city is really stuffed things to do related to art, music and history (and food). Bologna is a mixed bag when it comes to loud and dirty. There are quiet and elegant parts of town (around the piazza Santo Stefano, the Spanish college), but it can get pretty rowdy and trashy right around the university. Day trips from Naples are more outdoorsy and subject to weather than ones you might take from Bologna. There is genuinely lovable food in both cities -- and if you choose Bologna, you should definitely head to Parma for one of your daytrips (where there are many lovely things to see as well as eat.)

You are right that there are often blue skies in Bologna in December. The typical weather pattern is a rainy November, with often a sunny lull until you start closing in on the short days of December, after the 15th, when winter is very much on its way. You could get rain though in November, or even light snow if there is a cold snap. (You will almost certainly have some fog.) For a 4-day stay, you'll have to take what comes wherever you go, and Bologna is generally well set up for the cold and rain. Naples less so.

The train station area (which includes I Portici) is only a 20 minute walk to the piazza Maggiore. Historic and atmospheric areas like the Jewish ghetto and the university area may be a tad shorter if you take some shortcuts. If you are thinking of day trips, the train station area is convenient. My main concern about that area would be double glazed windows to cut any traffic noise.

If you are seeing favorable prices for Bologna hotels that you like, that's great. I have eaten at I Portici's restaurant, however, and don't recommend it. If you end up staying near the train station, I recommend a short cab ride to Antica Trattoria Della Gigina.

http://www.trattoriagigina.it/