??? How Much Would You Spend ???

I will spend all your money if you let me. 

the real question is: how long will it be before you want to upgrade 

In my experience, speakers make the absolute biggest difference in how your system will ultimately sound

I guess it depends. I tried a few integrated amps in the last few months with 2 sets of speakers. They sounded profoundly different. I practically could not tell in a blind test which speakers were on, although I thought I could recognize them from a mile. (Other than volume, there is a 5db sensitivity difference)

But in general I agree, to find the speakers that sound the best to your ear is where to start. 

Questions like this are about synergy not dollars which is why they are impossible to answer without knowing specific brands. So what are these speakers?

More money doesn't mean better. Go get a Buckeye Purifi and you're set for life. Nothing will sound better.