"first of all does anyone have any experience witht the 1966 Barros Colheita?"

I sure don't.

"I know 1966 was a great Vintage Port year. Does this hold true for the Colheitas in general?"

What we must keep in mind is that vintage ports and Colheita ports are completely different animals.  What makes a great vintage wine is not what makes a great Colheita wine.  IMO, declared vintages should not be a real consideration when buying tawny ports, which is after all, what a Colheita is basically.

"Final question. 1967 was not a vintage year, but colheitas were still produced. Does the quality fall offf that significantly?"

See the above.  This wine was in oak for 40 years.  What the vintage wines were like has less and less influence over time.  IMO, the influence of a declared vintage may have more effect on saleability and price than on the wine you will drink.

AFAIK, Barros is known more for it's Colheitas than for vintage wines (tho' I have only had their vintage ports).  I would have to guess that any house which could produce significant quantities of quality vintage port in a declared vintage would do that as opposed to producing a Colheita.

it is simple economics.  Port houses started getting a return on that part of the  '66 grape harvest which was made into vintage wines before the end of the decade.  Grapes made into Colheita wines and barrel-aged for the next  40 years cost them money every year for 4 decades.  Don't even have to do the math.