The quality of a rebuilt Steinway depends on who did the rebuilding. Since the quality of new Steinways, as well as those rebuilt at the Steinway factory, varies a good deal (read Larry Fine's description of Steinway quality control), a rebuilt Steinway can easily be a better piano than a new one.
One thing you need to be clear about: a rebuilt piano is, properly speaking, a completely remanufactured instrument with an expected life and level of performance equal to a brand-new piano. If your rebuilt piano includes a new soundboard, strings, hammers, pinblock and an action with all worn parts replaced, the it is truly rebuilt. If it has the old soundboard and pinblock, etc., it is what is properly called a reconditioned piano. Because the cost of rebuilding a piano is very high (roughly equivalent to the price of a new grand piano), uprights are very seldom truly rebuilt.
Also, a rebuilt Steinway can be just as much the real thing as one directly from the factory. The basic structure of the piano and the scale design remains Steinway. The "Steinway sound" is potentially there.
Over the years, Steinways have had a wide range of quality of parts. A replacement part manufactured by another company might well be better than a "genuine" Steinway part.
The question of quality in a Steinway always depends on the individual piano, even more so than with some other makes of pianos, since Steinway's quality control is quite variable.
In terms of taking some sort of financial "risk" with a piano, I don't think pianos should be looked at as some sort of investment. Pianos are musical instruments; don't confuse the two. If your rebuilt instrument is a good one, and you like it, and you hire a technician to survey it or the dealer gives you a new piano warranty, then go for it. It will serve you well as a musical instrument (but probably not as a financial investment).