I suspect that sooner rather than later you'll want to upgrade the center and as you point out it makes good economic sense to do that now.
I have had an epic 80-800 system for nearly 2 years, and the one speaker that never quite seemed up to speed was the vp150, despite its very nice sound. Hopefully by this time next week the vp180 will have taken its place.
A final consideration would be the size of your room. It was recommended that I install dual vp150 centers as well as dual subs in my size room (approx 8,000 cu ft) and I could not afford either at the time, so I put those on the upgrade later list. Now I'm told that a single vp180 will fill the bill, and I suspect it will, since the vp150 has been quite good, I would say close to sufficient.
