The roundabout project in Washington State incorporated all of that (pedestrian,bike path) I believe. A roundabout moves traffic, prevents t-bone collisions, and can eliminate the need for additional lanes (395 at 30-A would be right turn lane Westbound, protected left turn lane Eastbound). Either way, right of way would have to be purchased at fair market value by the county. Probably not going to happen...unless locals and state put up some money, as was the case in Washington State.
There are other methods of reducing gridlock at intersections: add a lane. This does nothing to calm traffic in my opinion.
The ideas of more perpendicular avenues between 30-A and 98 is dangerous to the protected forest areas and/or invites more development in the area(s) if any,
that are not protected.
Again, the problem, to me, would be the bike path. As it stands now, the bike path traffic does not merge with the vehicular traffic. If a roundabout was installed, it would become necessary for the bike traffic to merge with vehicular traffic to keep things flowing. I can't see the "typical vacation bicycler" (many of which are children) being able to merge with typical vehicular traffic.
Also, I don't see why north-south "connector roads" can't traverse the forests and be restricted from any commercial development. You see scenic roads through parks all the time.