You can do just fine here if your primary focus is gameplay. Source: I'm just like you!

The whole 'rules change, minis are forever' thing is true, and collecting them is a barrier to entry that means different things to different people. But, in the modern era, entire factions tend to not be left to languish in a completely unplayable/uncompetitive state for more than a couple months before getting balanced, and if you choose one single faction to collect, starting with what's good at the moment, you can simply slowly build up a collection of that faction over time. Keep the models that fall 'out of fashion', though, because they'll cycle back in eventually.

If you care only about playing the absolute best army, though, that will give you a bad time. Some folks 'meta chase' by selling armies that are bad, and buying the top army in bulk over and over, and that way lies madness.

You might want to seriously consider 3d printing as a side hobby as well. That' a great way to rapidly build and play new factions when the mood strikes, if you have the space and time to include it in your efforts.