A lot depends on what you want your car to sound like. If you're like me, I grew out of my 1995 4- 15" setup for more focus on staging/imaging and tonality. Try going to some MECA IASCA events to hear some professional built cars then ask some questions about the equipment they use. Or maybe try to meet up with some CA people locally. Listening to a variety of equipment is really the only way to know if you like SQ ( sound quality) or loud or extra bass.
You can get a competently designed and built amp for less than $.50 a watt (compared to good 90's equipment at $2 a watt or more). Leaves more room to spend money on speakers, which, with an expert install, will yield the most gain in SQ.
Oh, and the only thing that hasn't changed, is that you will still spend more than you had planned.