No problem whatsoever going into a restaurant alone. The more highbrow, the more you should expect excellent service even as a single person,. Some great restaurants have tavern or bar seating and menus that might be the best of both worlds for you and often don't take or require reservations, At the best places, you'd need a resrvation for a peak time table,even for one person.

Not sure what dressed like a tourist means as many New Yorkers paid people don't wear suits (lots of tech, media and fashion people around here). Very few places would expect it, and in many places you'd look out of place in an "out of town businessman" getup.

The UWS has many casual restaurants frequented mostly by locals, many have bars too. But the standalone bars in the area are often college bars, very young and loud.

NY also has restaurants that specialize in single foods so mac and cheese places, rice pudding, peanut butter etc.

Thanks for your reply nyer.

I think I could brave the odd college bar! I wouldn't be averse to reliving my youth for a night or two. I'm only 32 (I know my first post probably didn't read that way)

In terms of dining alone, would I be expected to tip a little more? Or is it just the luck of the draw for the waiting staff as to how many covers occupy a table? In the past when dining alone I think I have tipped rather excessively because the food was usually being paid for on expenses.

Eater usually does a good job of listing the top foodie spots around the city.
http://ny.eater.com/archives/2013/01/eater_38_4.php

Also, a few recs:
For burgers, try April Bloomfield's Spotted Pig
For steak, try Minetta Tavern and BLT Prime

Enjoy your trip!

Certainly you should not feel bad about taking up a table for two. However, in mentioning "bar seating", nyer meant that you literally sit at the bar and have your meal. This is often a great option for a lone diner. Even the nicest restaurants will offer this as an option, and set the "table" for you at the bar, with cloth napkin as placemat and full place setting. Then you get the attention of the bartender and can chat with your neighbors if you like.

Thanks for the feedback. I think I'd be more comfortable with the bar seating option so that sounds like something I'll pursue.

I am looking at trying some of the prix fixe lunch menus at the higher end places just so I can afford to fit in more 'splurge' type restaurants. I have been recommended Asiate at the MO which looks like it has a good lunch deal.

As a single diner, tip what you feel like tipping. Average in NYC is probably 18-20%. Absolutely no need to compensate for not having a second person at dinner. You never know how much a party of 2 would be ordering. Maybe they'd actually spend less than you do, or even more likely, take up more time than you would.

Lunch at some of the better restaurants can be an amazing bargain as you've seen.

I don't think I've ever heard of a "high brow" restaurant. Learn something new here every day.

One very good and popular restaurant which has a lively bar area dining scene is Maialino, in the Gramercy Park Hotel.

Past bar age, I'm afraid.

For solo dining, I really like the momofuku restaurants, especially ssam bar. If you really want something special, momofuku ko is awesome too, but reservations are hard to get.

The upper west side has a tone of restaurants with both bar service and outdoor cafes which you should consider for people watching. Just explore some of the opportunities that may be a little different - like Kefi for great Greek food. And you often see single diners, although sometimes they would go earlier than the standard 8 or 8:30 pm. Walk up and down B;way, Columbus and Amsterdam for a bunch of modest to moderate choices.

For bars the UWS has a bunch of casual places - either neighborhood or - further uptown, college. For other places around the city - have a look at Time Out NY website. Has a list of a lot of places with music that are not dance clubs.

For a dive bar with music, I really enjoyed Bar 55 in the West Village.

Thank you for all your advice and feedback. I'm looking forward to my trip more than ever.