Once links are removed can be lost PR gained.

Is better idea to go with a link building which won't die (links not removed). Probably same costs but benefits double:
- you can gain probably more direct visitors: more likely to get from link directories than from forum signatures, more likely to bet much more with preserved links than with 2 months available links on forum signatures
- you won't loose the links/PR

So i think it worths to do some healthy link building because it would help much more.