Hello Audioweb,
A very good amp will give a more effortless and dynamic sound with more headroom and faster stops and starts. Even efficient speakers can be tough on an amp and the receiver, in spite of it's specs, will still bend under pressure with all channels in action.
I've found that speakers that were seemingly well fed really thrived with a dedicated amp. For example, years ago I was running a simple system with a Denon 3200 driving 5 x M&K S-80 speakers (small 2 way, and crossed at 80 hz to an M&K sub ...so the receiver shouldn't have had *that* much work to do). I hooked up a 5 channel amp, I can't remember what they're called, ATI or ATC or something like that (parent company or bigger brother of the Outlaw brand ?),...it was a very heavy 5 x 150 watt amp and it really transformed the system. The sound just lit up in a way that made me giggle and the dynamics were now frightening instead of mearly (sp ? Sorry !) impressive .
Having said that, processing is also important in HT and I don't know that much about your Rotel (though I'm guessing it's pretty good). You might also consider going to a bigger/stronger receiver with newer A/V chips (?); something like the Pioneer 49 with self calibration (circa $2K on Ebay), a Denon 4802/3 or 5803 used ?
As far as amps to try,...with the Klipsch and their tendency toward a dry sound, you might look for warmer (mabey darkish sounding) amps, mabey Sunfire or Classe rather than the amp I was talking about (ATI ?) or Bryston (though I like, have owned and currenty own Bryston, they'll not work to warm a system.
I don't disagree with the advice you've been given so far,...just thought I'd ad that it *can* be worthwhile to add a nice amp to a receiver.
...One other advantage is that lightening the load on the receiver's amp will probably make it's pre/processor functions better (amp not draining the power suppy all the time etc.)
M