all depends what you want it for and what surface its on, if its a grassy field then 4wd is much better, although 2wd is good fun.
Ive got a losi 5T and a baja, so i love the rugged go anywhere losi, 4 wd monster, and the baja which is ace fun drifting the back end out, i think there's a little more skill in getting the throttle right as too much and it goes round and round. The 4wd much safer and planted.
Saying that though if you look at some of the monster ones on here with 12 S, All down to personnel choice my friend.
The spares cost debate depends how daft you are, most of the buggies, trucks etc are pretty well built these days, but if you drive anything into a lamppost at 30 mph then most things will break !!
Good luck