Not a bad plan.
At one time, I compared Rotel separates directly with a Rotel receiver. The separates sounded better, in fact, I bought them (for a week, then upgraded to a Classe preamp, continuing to use the Rotel amp). The salesperson I worked with said that the Rotel integrated (which they didn't stock) sounded more like the receivers than the separates (this was certainly true of the other integrateds I auditioned). So if that is any guide, yes, you should see an improvement by using an external amp.
The unknown factor here is, where is the weakness in your current integrated -- the preamp or the amp? Probably both. In other words, eventual purchase of a separate pre-amp would also make a big difference (preamps make an even bigger difference than amps in my book). But hey, Rome wasn't built in a day, and improving one piece at a time works for me.
I haven't listened at length to your speakers (I have listened to a lot of other B&Ws), and I rarely disagree with Sugarbrie, but I will go out on a limb and disagree about requiring a speaker upgrade. I think your CD player (which I have heard and like) and speakers can do a lot better for you than they are doing now, with better amplification.
My current speakers are the oldest part of my system; I got them used; they were new 10 or 15 years ago, and sold for around $1500 then (Celestion S300, I paid $700). I first hooked them to an old receiver, then to a variety of mid-fi separates (such as Rotel), and now to Classe preamp and amp. With each upgrade in amplification, they sound better and better, amazingly so. The biggest improvement I noticed when I switched in the Classe amp was in the bass, much tighter and better defined.
Last week I demoed B&W CDM-9NT speakers with a Rotel HT receiver (one of those foot-high monstrosities). They sounded awful. The bass in particular was practically unlistenable (to be fair, I had just been spoiled listening in their very nice 2-channel room), it sounded positively distorted.
So in summary: I think separates will make a difference for you, and so this is a good step in the right direction. The Rotel amps are a great value and give good sound for the money, so I think your plan is a good one. You can get a used Rotel amp here very inexpensively, $200-$300. Just be aware that you will probably want to go the preamp route when funds allow.
One last thought -- if you are buying from a dealer, see if you can borrow an amp to try this with, which will answer the question definitively for you.
