How much discount typically for a new MC275 to expect from a dealer?

There is no new Mc Intosh available now. It is replica and sound is not as good as vintage one.

I ALWAYS like to buy a demo piece when available. You still get the Warrantee, which you occasionally need to use. But that can happen with sealed-in-box components. The most common issue could be used speakers with very small cosmetic flaws. If there's a few small marks made by speaker cables in the back, I'm not concerned. Or there's a small tear in the grills, but the dealer will replace one or both at no charge. A tube amp could be bench-tested for 3-5 days under a load,
and if it meets ALL of its specs, who's to say its "used"?
I can't comment on vintage tube amplifiers sounding better, but Night-and-day or just "different"?  

I can't tell you the name of the dealer here. They have always given me 10% and no sales tax because the state they are in is tax free. If you buy 2 pieces, you will get 15% on the second one.

 It’s the way you work it. I’ve always received 20% off of McIntosh gear from my dealer. I also don't pay sales tax if I pay cash. The deals are there and don’t let them tell you otherwise. I won’t buy any new audio with less than a 20% discount, as if I want to sell I’m not taking a major hit. As others mentioned if you can get the demo model it’s much easier to get a discount as well. I recently purchased a pair of speakers and had to take the floor model to get the price I wanted. But with original boxes, pristine condition and already broken it was a better deal than new. 
 

McIntosh offers a 3 yr warranty for new equipment.   I am sure you can find a used but mint amplifier that is less than 3yrs old- and probably less than a 1 yr old- for 25% less than msrp.    Buy used, still have a warranty.  Best of both worlds.    Most problems manifest in the first few months of use.