My 2 cents worth
people starting out modeling want to model what they had , their friends had , or the one they couldnt afford
this being said many adult modelers who are now in their late 30s or early 40s probably started out driving in one of these oversized slow and boring cars and their should be a decent demand for some of them at least. (hows the revell 77 monte carlo selling)
while i agree the monaco caddy and town car would most likley not be worth the investment of tooling , the 73 grand am , lemans gto might , and i tend to think between police cars donks and lowriders a 77-90 impala caprice would sell rather well and have the added bonus of appealing to some younger folks