I like the idea of a party of adventurers having a base of operations. Players are often reluctant to do so because DM's love blowing that kind of stuff up. So these are some optional rules for 3.5 that give players a reason to buy the stuff. If the DM makes an explicit social contract with the PCs to not mess with it too much, the players might even buy the stuff! It's up to you whether the PCs enjoy these benefits if they're traveling to the other side of the earth or whatever -- a really expensive wagon or ship might boast a limited number of the accessories, at your discretion.
Buying a suitable building costs 1000gp. Additional purchases that have game statistics are as follows:
Fancy Samovar (800gp): +1 initiative to entire party.
Laboratory (800gp): +1 damage when using poison, and 10% discount on potions and scrolls.
Sauna (800gp): +1 max HP to entire party.
Trophy Room (1500gp): +3% experience per session.
Library (2000gp): +3% experience per session.
Grindstone (2000gp): +1 melee damage to entire party.
Fine-Tuned Scale (4000gp): +5% value of raw GP treasure found.