Mitch,
Yes they are, but the prices vary according to box type. Is it all 1/32, 1/72 or a mix?
Not too clued up on 1/72 stuff, but reasonable condition box sets can go from about £5 a box for the 1986 14 figure boxes, to £15-£20 for some of the 72ish brown boxes and 73 onward 'target' boxes. The majority of the 29 figure large boxes go for between £10 and £15 if in reasonable condition.
There are some that tend to make more due to the relative scaricity. These include the 1983 14 figure boxes of Afrika Korps, US Paras, SAS, Modern NATO and Modern Russian figures, which werre only released for a couple of years at a time when toy soldiers were becoming less popular.
There are a few other odd rarities here and there as well, the 1981, 14 figure Napoleonic French Infantry is fairly scarce, and one of the hens teeth sets is the original 1968 1st edition Brown box of (Brit) Paras (which are the upsacled version of the 1/72 figures - pretty crude figures but price hiked due to being the first of that series). These can go for £100+.
There are a couple of good comprehensive sites dedicated to the 1/32 range. I'll dig out the site addresses and post them in a bit.
Cheers
Simon