This business plan is flawless! How do I invest in it?
You can slaughter them in their base, which will net you quite a few caps from the Denarius' and Machete Gladius, plus whatever the Praetorian Guards use. Once you wait a while, more should spawn, but not in the numbers they were originally. As far as I know, all the other Legion Camps do not respawn once they are eradicated. Not a great cap-making method though. It's easier to just gamble, play caravan with people, and do side quests. I had well over 150,000 caps by the time I was level 25.