Grand Pianos are definitely worth it! They look good, they sound good, and when you play them, they feel good. (compared to most uprights, anyway) Best purchase ever made.
Does the length of the piano have much of an impact?
35 000 USD will buy you a VERY nice piano! I think you might be able to look at a Petrof or a Yamaha grand over 7 feet.
It depends on the size of the room you are going to put it in. What size grand were you wanting? A small grand in a big room is probably better than a big grand in a small room.
Also,
what floor material is in the room? If you have solid wood floors, Yamaha might be too bright.
I think Kawai sounds terrible, no matter how well it is tuned or where it is sitting, so be sure to stay clear of them. (IMO anyway)
35000 isnt quite enough for a Steinway grand.
Should I buy second hand or brand new?
About 2nd hand pianos: Sometimes you will see great deals, but most of the time, the person who is getting rid of the piano is doing so for very good reasons, so stay away. For example, a beautiful piano that has been sitting in an old lady's house for 30 years, collecting dust and has a bunch of crap like picture frames sitting on top will not be a very good buy. Chances are, every part of it has gone downhill and will take a lot of money to get it restored. (tuning, part replacement, warped soundboards from improper humidity, etc.)
However, there is a downside to buying new ones: Salespeople. Most are unethical, immoral, and will do absolutely everything they can to get you to buy the cheapest piano at the highest cost. Simply put, they really don't want to find the best piano for you that suits you; They want to find a piano for you that suits them and would result in the greatest profit. Watch out! They can be very tricky (even putting time limits on "special" offers made "just for you, because I like you"). Learn to say "Ok, well, thanks for quoting the price. I'll just check around some other places." It is such a powerful blow to salespeople when you walk out of the store. When you first walk in to the store, they will assume you are a fool, so prove to them you aren't and you will get great deals in the long run. Don't be in a rush; If you are desperate to buy, then the salespeople are less than desperate to sell.
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final piece of advice: Go to the library and get a copy ( hopefully, the most recent edition available) of
Larry Fine's "The Piano Book." He has so many great tips on piano shopping. He even tells you how to talk to salespeople to get the best bargain possible. (I think I used some of it in my response on new pianos above) A bit from the book that really helped me while shopping is when he suggests phoning places in the next city over to get prices. This is especially helpful when a dealership (ex. Yamaha dealership) has a monopoly in your city. (I saved 2K by doing this)