Depends on price.
I wouldn't think that no rebuild history would be a HUGE issue with the bike so long as it is factored into the price. 2 strokes need semi-regular, cheap top end rebuilds for optimum performance anyway, so whether or not it's been done already, you will need to do one sooner or later.
I'd certainly check out what else is around, if you can find an RS125, I believe they're a better bike - more of a pure race rep, whereas the NSR150 is more of a commuter bike with a 2 stroke 150cc stuck in it. Or so I've heard.
If you want a honda, try find an NSR250
