I'll assume that you've got the 'outdoor' Bose 151s on your tower and are asking about the marine Bose 131s.
I've been designing my system, and after I had it all figured out, my wife convinced me to just put 151s on the tower. I told her that since the 151s won't look as cool as custom carbon (homemade) bullets, that she'd have to let me upgrade the boat speakers with 131s. We'll see if we've got any refi money left ;-)
I've heard nothing but good things about the 131s. There are very few 'door' speakers that include their own enclosure, so you've typically got to either build your own, get "free-air" speakers, or just learn to live with distortion at low volumes.
Take the Epics' stock Kenwoods for instance - the speakers aren't that bad and they're not totally underpowered, but they do distort pretty early. My forward speakers produce more bass than the aft ones, and the aft ones distort earlier. Audio weenies get real serious about their enclosures, but at the very least, we should make an effort to enclose the stock speakers. I beleive that if an audio weenie was going to use 6.5" speakers, he'd probably use a crossover to remove the low-end tones and use the speaker as a mid- and high-range (the 12's in the trunk take care of bass.) If you did want to run the speaker full-range, the enclosure volume would be something way under one cubic foot.
The 131's have their own enclosure built right in. It's ported, built by well-funded audio weenies & are documented well. They come with 3-year warranties. They'll cost you $238/pair at every single store (except maybe the Bose outlet). They handle up to 80 watts RMS (which is a lot more than most of the "100-Watt" marine speakers you see out there), and from what I hear they are very well-liked by their owners. One of the best things is that you don't have to wonder about enclosures or expect any kind of distortion.
I'd like to hear your thoughts on the 151's when you get a chance.
