My density? I'm 6'1" & 225/230lbs, I'd say fairly bouyant.

I haven't tried it wearing a 7mm full suit though. But I have done it several times wearing a 3mm full suit at 20ffw on a training platform. I've never been in a situation where I
had to take it off while submerged. But like I said, I routinely practice it as well as other skills in a local quarry. A 7mm suit would definately make it more challenging, but I think it can still be done. As long as you don't let go of the BC you will still stay down. What I usually do is get negitively bouyant, and doff the BC, left arm first then the right arm. I keep the reg in my mouth at all times and lay the BC down with the tank down on the platform with the tank valve towards me. By the time I do this, I'm verticle in the water with my feet above my head due to my body being bouyant. I then just put my hands through the BC's shoulder straps and grasp the tank. Then just pick the unit up, over my head, and onto my back. As soon as it's on my back, my feet come down and I hook all the straps back up. It takes practice, but so does most other things scuba related. This was a
big focus point during my O/W instruction. Our instructor insisted that everyone be able do it. We all used weight-intergrated back inflation BCs in the exercises. Sure it's a little unsettling when your feet go above your head and you get the sense of losing control, but as long as you don't let go of the BC, your bouyancy as a whole doesn't change, just your position changes. If I were wearing a 7mm suit/drysuit though, I probably would wear a weight belt, but mainly to spread all the weight that would be required out.
As far as when I put my weights in goes, I always put the weights in the BC prior to donning the BC. But I can physically handle the BC with weights, so it's no big deal. I've yet to drop weights. I've seen others put the weights in after entering the water and haven't witnessed any dropped weights as a result. But I've seen people forget them altogether and try descending without them.
The seas get rough here too, but the charter boats have a place to sit down and donn your gear(at least the ones I've been on) and rough seas are only a problem when you get up and make your way to the entry point. But I don't see how that's a factor in this discussion, since a rocking boat is difficult no matter what kind of BC you have.
Accidental release? With the Zeagle BCs, the BC I use, it would be virtually impossible to accidentally release the weights. You have to physically pull the Rip cord which is also held down by velcro. Sure you could hang it on something and possibly release it, but you could just as easily hang a weight belt buckle and release it.
Which is safer? I feel that safety comes with being properly trained, being comfortable, and having fun on the dive. I'm properly trained for the BC I use. It being weight intergrated makes me more comfortable because I don't have to deal with a weight belt getting loser as I go deeper, hurting my sides, nor weights shifting around. Being more comfortable also makes the dive fun.
Which has most cost-value? That's user preference. I think weight intergration BCs are because of the above reasons, but they are generally higher.
If I were engaging in tech dives, cave dives, or something of that nature then I may not use intergration features for some of the reasons you pointed out. But IMHO, for the everyday Recreational Diver they are great.