Firm feel reinforcement plates worth it?

It's worth it to do the reinforcing, absolutely!

Whether or not you buy the plates or not is up to you. I bought a Firm Feel kit that had all the plates to reinforce the K member and box the steering box mount off of eBay and used that to reinforce the K member for my EL5 Dart. When I reinforced the K for my Duster, I just made the plates and used washers around the strut rod mounts and LCA pivot sleeves. I probably spent about the same amount of time doing both K frames, even the one I made the plates for. Seam welding the K frames go a long way for stiffening things up, and I think reinforcing the steering box mount and LCA pivots makes sense for EVERYONE given how often the LCA pivots tear out of the K and the number of times I've seen a cracked steering box mount.

The LCA plates I've bought a couple times for my various cars. It's not that I can't make them, its just that for $30 they look a lot nicer, and I don't have to spend time making them.

If you're even considering those reinforcements, get 1" torsion bars. Even if you currently have V8 bars, those will be a MASSIVE improvement. Rubber bushings are just fine, especially for a street car. 225/60/15's will fit just fine on cop rims, that's what I have on my '74 Duster...