I've been running 25s on my mt R1850s and it's getting to be time to buy another set of tires. I ride on a lot of chip sealed or just rough tarmac. It is worth the $$ from a comfort standpoint to get a set of wheels built to run 28s? I'm 6'4" and weigh 200+ so I have to keep my tires hard or I pinch flat (or in the case of my tubless MTB bend rims) .
I'm pretty skeptical that they would help much but thought I'd ask for experiences.
I'm running Ultegras. They are tight getting a 25 in and out with the cam open, havne't looked to see just how close the clearance is in the top. I assumed I'd need to rims because I'm pretty sure I could not get an inflated 28 on and off and still have the brakes adjusted.
Being a bit taller and heavier- I can say that there is no doubt a 28mm tire is more comfortable than a 25mm tire.
A 28mm tire has something like 25% more air volume than a 25mm tire. Pretty significant for only being 3mm wider.
As for the rest of your posts- I dont follow at all. A new wheelset wont allow you to mount 28mm tires onto your frame and easier than your current wheelset. If 28mm tires fit your frame and fork, but you just cant get them thru the brake calipers when inflated, then dont inflate the tires until the wheels are mounted. Pump a few times to seat the tire, install the wheel, then pump up the tires. Pretty simple work-a-round.
You cant get a smaller wheel to offset the size of the larger 28mm tires. <---this looks like what you are wanting to do, i think.