I agree with all the reasons for taking it off. I just did my 5 speed. I got the kit from Hitchcocks which included the tap, case to block gasket, hardware, seal for the gear change shaft, a new cover seal, and the gear.
Including using a tiny gel cell for a battery, I have a net weight loss of 25 lbs.
The previous owner of my bike went through considerable time and expense to make it as close to the way the 55 rolled off the line when it was still English as he could. The one thing left to do was get rid of the hump. Now the only evidence is where the starter bolted to the block. I guess there's not much I can do about that.
In hindsight, I should have done a right shift conversion which would have allowed a more period correct primary cover, shift and rear brake controls.