From personal experience, full suspension is nice to have but only really great for guys with really deep pockets. Most FS bikes arent still going ten years or so down the road, but the C+V forum is filled with bikes that are MUCH older. The reason for this, besides the relative newness of FS, is proprietary parts that get hard to replace (most typically bushings and often the shocks themselves). Those parts are more likely to break under the weight of a Clyde than under "normal" use by a sub 220lb rider. Forks can almost always be replaced at one point or another. If I were you, I would look into an upgraded fork or even a rigid fork for that 4300. My fiancee has a 4300 and it's plenty of bike for her, and enough bike for me (if the frame was my size). I used to ride a Specialized FS rig "back in the day" (it was a '96 MY that I upgraded quickly with XTR parts), and that Trek 4300 is except for the fork equal to or better than my old ride in most aspects. From what you've said so far, your 4300 could probably stand to get a good service along with a new fork, which will be a good deal cheaper than a new FS bike, which will allow you to save even more while you lose more weight and get into something REALLY nice down the line.
Just my .02, and the plan that I'm personally sticking to at the present. In my case, my bike is a HT pre-Pacific Schwinn Mesa. It's not new and it's not perfect, but it gets the job done, and I'm sure your 4300 can be adjusted to do the same.