they're not usually worth buying full sets at once. for a full set, most sellers will ask for the same cost as the best prize you can get (example: for Neopia Central 1, they will ask for about 340k, which is the same cost as the best paintbrush you can get from it). of course, you might not get that prize and it won't be worth it.
however, if you have time or SSW, you can randomly search for pieces that you're missing. pieces might sell in shops for 7000-12000NP, and these are usually worth getting. i would never pay over 20000NP for a single piece unless it was the last one i needed
of course, if you're gonna invest in the WC, you should really earn the 3 pieces a day that you're allowed to. it makes a world of difference =) and it's fun!
oh-em-gee, i have a wikipedia page!!!!
http://en.wikipedia.org/wiki/Bumpty :-D
April Goals: (progress)
125 Boost S/D for Stami *check*
Finish NQI Evil *check*
Shop Size 160 (current: 210) *check*
NP till main market: 14.5 million =(