I know almost nothing about the speakers you have, but it's not at all clear that replacing all 5 for $1500 is going to result in a major improvement.
The rears are typically less critical, so you'd probably get a larger overall improvement by leaving the old rears in for now and spending your budget on upgrading the other speakers.
You didn't mention a sub, so I'm assuming you you don't have one? A quick review of the published specs for speakers you have suggests that a lack of bass is probably your single biggest weakness.
Is there any way you can switch to freestanding speakers for the front? For example, if you swapped out the fronts for BMR Philharmonitors (link below) you'd have a solid start on decent system. These have solid bass response, so it would help with that (assuming you don't have a sub). Granted, you'd probably want to get a sub at some point, but at least you would have some useful bass.
In my opinion, the thing to avoid is making a never-ending series of minor upgrades buying equipment (e.g. speakers) you still do not like. This ends up costing a lot more than replacing one set of speakers at a time with good speakers.
Philharmonic Audio's BMR Philharmonitors use a 3-way design with a very special driver outlay that has audio enthusiasts excited about the potential performance advantages that it could offer Read on.
www.audioholics.com