I guess it comes down to how much you mind fishing in dirty weather.
I don't have a stand-up cover on my boat either, and 99 % of the time I wouldn't want one, but I do have a good Gore-Tex rain suit and don't normally worry about how much it rains, but must admit I've been jealous a few times on cold snowy days when I see someone cruising by all covered up & dry, and I've got icycles hanging off my mustache.
The covers are a pain if your casting, but can be awesome when your trolling in nasty weather.
I normally fish with Squid in the cold months of November & December and some days his covered boat is worth a million bucks