Q: If I wanted to spend ten to twenty thousand dollars on original art, both as an investment and to decorate my house, what should I buy, and why?
A: It depends on if you want to make a “safe” investment or a more speculative one. One gets less when buying the work of a “name” artist than that of somebody relatively unknown, but the possibilities for appreciation are higher in the latter instance. Since you will be buying art for your own pleasure as well as for future sale, I would suggest that you look around the web for art you actually like, and wouldn’t mind seeing for a while. That way you will be happy with it even if its value does not increase. (Of course if it does, you could be even happier.)
Many artists are selling their work directly through the web, without the usual 100% gallery markup, so you would save money to start with. For what you are proposing to spend, you can probably get ten original pieces of art by the uncelebrated-as-yet; and if any of the ten becomes well-known, you should do quite well. Even artists that are well-known today may be less well thought-of in the future, and their prices may decline.
Additionally, art is not easy to sell, so liquidity is an issue; remember you would most likely be buying at retail but having to sell at wholesale If you decide to take my advice and check out what the web has to offer to the would-be collector, you should of course take a look at my work (which is very reasonably priced and can only go higher).