Are there actual decent wineries in this area? We are considering a last minute trip from Chicago driving out there. in the next week. Any other recommendations for areas to stop?

I've been to the island of Martha's Vineyard many times...never been to an actual vineyard there or on the cape. I have tasted wine from Chicama Vineyards, and it was only so-so, IMO. But my standards are high because I've visit wineries in Italy.

Of course this subjective...not sure what constitutes a 'decent' winery. I have talked to people who enjoyed visiting a winery on MV but they didn't speak as if it was the highlight of their trip.

On the Cape there is:
www.trurovineyardsofcapecod.com

On the way to the Cape there is Westport Vineyards:
www.westportrivers.com
(Their sparkling wine is actually pretty good

A little detour on the way to the Cape in Little Compton, RI:
www.sakonnetwine.com

I would say the locations and settings of these wineries are better than their products...

There is a vineyard in Truro. www.trurovineyardsofcapecod.com . And one in Falmouth www.capecodwinery.com

My cousins are avid Martha's Vineyard fans...they're really looking forward to the "harvest fest" this year. I went with them a few times to various tastings but never found the wines up to par (I agree with Ralphie). Then again I live near Napa, so...