Picking up just the encampments? Sure have a treasure hating deck that needs actions (e.g. Goons/Pool) but can sustain a gold (e.g. Haven). Running a tight ship of 6 Goons, a Gold and encampments is huge points (36 VP from buys alone on the final turn). Obviously that is a contrived example, but encampment can really limit the number of terminals in play when it is the only village out, monopolizing them can make for some lopsided setups. Other times you may want to limit your treasures and Gold just works better (e.g. with Legionary or to use as fodder for a Stonemason before buying it back).
Further it is completely valid to treat encampment as a mini-Madman. With light trashing and sifting you may well be able to setup 6 Bridges quick enough to skip out on the Gold/Plunder entirely. With 7 (from Nec) Bridges, that is pretty much game over once you line up the combo. Encampment, Forum, Bridge would be a not too bad a megaturn setup where Gold & Plunder may be skippable.
Outside of the megaturn, Encampment is dirt cheap. Drop a ferry on it and you can just buy replacements for +buys. This can let you haven enough actions to setup interesting combos (e.g. Militia, Masq, B-crat) and just buy two Encampments a turn off of non-terminal +buy (e.g. Forager, Cmaker, Pawn).
More often though, Plunder is just insanely good unless it is very near the end of the game. It is a non-terminal Monument for $1 more that you cannot even draw dead. Yeah it is vulnerable to thief, gums up Pools, clogs Libs, cannot be Kc'ed and does not juice Cityq ... but it takes very few turns for Plunder to pay out and it is cheaper than gold to keep your cheap "Lost cities".
Ultimately I think Encampment is good enough that you should just plan on buying it back a few times unless you can make a go of it with other villages, heavy trashing, or non-terminal draw.