For me, any interest starts with the historical period (I rarely move outside my comfort zone of historical gaming). If I’m not interested in a period, neither figures nor rules will tempt me.
If I’ve decided I want to game in a new period (increasingly rare as I get older!), finding suitable rules for what I want to do comes next. I have used proxies, card cut-outs, or persuaded friends to play games with their figures using a ruleset I think will give the game I’m looking for. Only when I think I’ve found a suitable ruleset will I start getting figures. The figures are going to be the main outlay, in money or time. Of course, sometimes I think I’ve found the right ruleset, bought the figures, then decided that the games aren’t giving me what I hoped for, but since I’m interested in the period (my starting point), I just have to go back to the rules search.
I think it is interesting to see how many voices in this thread put last the decision about rules. I can understand the thought that rules are ‘transient’ but I couldn’t imagine putting in all the effort to assemble armies, if I didn’t have a very good idea how they were going to be used.