This is gonna sound , but I've had the original stock suspension on my baby (1999SE-L) since day one. Granted, the car does not feel as tight & stiff as it did when I drove it off the lot, but nor is the ride punishing as would be expected when things underneath go bad.

At what point should I consider replacing stuff? And which parts (shocks/struts/springs) might go bad first? And what kinda $$$$ are we talking, assuming I don't DIY?

 

Springs generally never go bad, but shocks 100% will. Get yourself some new shocks to get that sporty feeling back:
http://drewm.dyndns.org/~drew/maxfaq...p?MaximaShocks

 

Replace the struts and get new dustboots while you're at it. If you want your car lowered, then get new springs. Shops will charge about $75-$150 for labor, but you can find some people from here who will do it for less. Also, after you get a new suspension put in, you need to get an alignment done so that'll be about another $50-$60