Heinrich's experience shows clearly in his comments
I'd like to add an example here, taken no less than from a commercial sim: SH2 was graphically speaking outdated when it first came out, the reason being its origins dated many years before. Since the development time stretched too wide over the original previsions, the game's appearence suffered a lot. However -and this is the important lesson- its graphics even if outdated would not have disturbed a good gameplay (if there had been any at all, that is) because it was a strategic game. The naval sims can take a hard punch in the graphics part and yet be good and addictive, unlike other genres.
So, choose wisely and stick with it. Even if you stretch development of other areas too much, a subsim game shall not suffer as much as other genres.