If I fund a wallet today and don't touch it for 5 years, is there a risk that I won't be able to spend my funds? Is it advisable to move funds around to a new wallet with each hard fork?
Despite the hard fork in March, 2016, setting a minimum mixin and effectively banning dust outputs (except as part of the coinbase, which is further going to change in the September, 2016, hard fork) we provided a "catch" that let users sweep their dust outputs at a mixin of 0. This functionality will be supported indefinitely, because maybe in a few years your 0.018293791 dust output is actually worth a couple of USD.
Similarly, any hard fork functionality in the future will have to, by necessity, provide a way for very old outputs to be spent indefinitely. We can and will deprecate APIs and client-side functionality, but we'd never prevent people from spending their own money.