It seems that you and I share similar tastes but I would suggest if you can watch some McHale's Navy episodes either on TV or online and see what you think before deciding to buy DVD's or not. I've tried to watch episodes but to me the show just isn't funny and I'm not really a fan of Ernest...
I also like 1960's TV shows, I enjoy many shows from that decade but McHale's Navy is not one of them and I wouldn't spend a cent on the DVD's. I guess I'm just not a fan overall of military themed sitcoms, Gomer Pyle USMC and F Troop are the only ones that I enjoy and I avoid all the others.