I have a 2500 and a Graham 2.2. I agree with what Twl says to a point. The main advantage the 2500/2800 have over your unit is their suspension. They are much better isolated from vibration. Your unit on a vibraplane(sp?)or some other type of stand that has high isolation characteristics would already be close to the 2500. I have no experience with the 2800 but if your that flush I'd get the top of the line Basis and be done with it.
If you don't have a super TT stand/isolation unit I agree you'd be better off upgrading the TT.
If you don't have a super TT stand/isolation unit I agree you'd be better off upgrading the TT.