There may be such a thing as too long of a "D-rest", but it wouldn't be due to anything related to the diacetyl, but more just if you were leaving a beer sitting long enough that it went through normal degradation of desirable characters.... if you left a beer sitting for 3 months, I suppose you could call that a continuation of your D-rest, but I'd just call that lazy...

Autolysis, meaty flavor from sitting on dead yeast cells. But, that really takes quite a while in homebrewing practices. Sitting on primary yeast cake for months especially at raised temps.

Yeah, not as much of a concern on a 5gal system as it is for the pros on a 30bbl system...

I tried it yesterday and wasn't satisfied. I thought it had a metallic taste and wasn't very good. Then a day later I had a friend whose is a better brewer than me try it and he said it wasn't bad, just maybe boring. I tried it then and didn't have the same bad taste as it had earlier, so I am just going to leave it in the kezer and see how it goes.

A little D-Rest never hurts in my opinion. Just to be safe.