Is this upgrade worth it?

There is a Levinson 333 currently listed at $3695 with a sale pending. According to the advertisement, it had a Levinson factory tune-up on 10/16/06. I think that tells the whole story of the value of this amp in relation to your friend's asking price...despite his amp being fixed and upgraded.

Whether the change would be sonically superior and suited to your tastes is only something you can answer.

From purely a dollars perspective, I'd suggest passing on his offer.

I'll second Tvad's advice, he made you an offer that you CAN refuse.

Second the above as, the Electros you have are good units anyway: it is not evident that they're flawed vs. the ML.

Third that. That should be enough to pass on that offer. Keep hunting, you'll do better...why not post anew and be more specific as to your needs or what you are missing in your present rig. You'll get the amp/amps to look for...IMO..warren :)