Front disc

An improvement over a worn disc, Yes, especially one that has the chrome wearing off unevenly, it is a bit lighter.
A performance improvement over standard good condition disc, No. 

I did the RGM master cylinder conversion using my own drill, tap and squared up on my bench drill. A bit nerve racking but don't risk it unless you feel confident of your ability. I then found out the disc was warped so bought a floating Girling disc but had to chamfer the bottom corner edge of the caliper to clear the disc rivets., no big deal as there's plenty of spare metal. Later on I fitted a braided steel brake hose, only for fear of the original rubber one bursting, the new hose gave it a firmer feel. The front brake now has good grab at town speeds but needs a harder pull at high speeds than modern bikes but I can live with it as it matches it's more sedate performance. 

Interesting details Adam. Comparing between Commandos I would have thought a floating stainless Girling disc with slots would not only be lighter and more corrosion free but better performing than the O.E cast iron disc.

I use twin Nissin floating and drilled stainless discs with Ferodo Platinum FDB88P disc pads. The initial bite, low or high speed braking in wet or dry is excellent, rear disc is also very effective with these pads but with a 14mm Brembo master cylinder.
Equivalent EBC FA27 or SBS pads weren't as good with the same setup, may work better with the iron disc.

I tried a similar method of reducing free play with the same binding result but only 1-2mm free play. Used a couple of modified Mk3 levers to experiment.
You can only adjust lever free play up to the point where the small reservoir bleed hole nearest the lever is still fully clear of the piston seal.

Both drillings must be unobstructed which is easy to see as the lever is operated, and there must be some free play at the lever. I now use 5-8mm at the lever end as per my Yamaha factory specs. This has R1 callipers retro fitted and my own 14mm m.cyl insert conversion. Couldn't find a similar Commando spec in the Mk3 or Norman White manuals.

Ended up using a standard Mk3 lever on my Commando, making sure the pivot is kept lubricated, the system properly bled and fluid changed every year. Works fine 40k miles later.

I believe it's due to the different Mk3 switches and master cylinder block, Mk3 lever has a more pronounced curve from memory.
 

non plated and drilled good

You might look in the Commando entries in the "Technical" section of the website, if you are on the lookout for general brake improvement ideas (although much of the content is quite old there is of course a sense in which it is timeless).

My current set-up is

• standard disc
• Lockheed caliper conversion from Norvil
• 1/2" master cylinder from a Kawasaki GPz 550 (n.b. some models had 5/8" cylinders)
• after-market adjustable dog-leg brake lever
• Stainless braided hose

More feel, less effort; can squeal front tyre (but it's a traditional Avon Roadrunner).

Nonetheless, it would probably disconcert anyone whose only experience is modern two-finger braking from massive discs and four-pot calipers.