The are two types of wear on the drive train; one is generic wear that is caused by just riding it (essentially the teeth are getting smaller), and the other is caused by elongation of the (aging) chain, and results in the hollows in the teeth getting elongated and deformed to match the elongation of the chain. If the latter is allowed to get beyond certain limit then fitting a new chain will cause chainsuck.
Instead of randomly rotating three chains, I would get one of those tools for measuring chain stretch (about £2), and when it reaches 1% fit a new chain; at that point the wear on the drive train should not be as bad as causing chain suck yet. How many times you can do that depends on the type of riding you do, the components you use, etc.
Having said that, in my experience by far most effective way of prolonging drive train life is by keeping the drive train clean; riding in the perpetual Scottish muck makes this difficult, and in this regard the Scottoiler is the best piece of kit ever. It looks sh!t, but it does the job like nothing else (the lube is water based, so the muck comes completely off without the need for degreaser); I have been using one for about 14 months now, and consider that the best spent £20 quid on the bike ever.