Walk on the un-runnered stairs for two or three months, then make a decision if you would ever want them to remain that way for eternity. If so, then less fasteners might be better. If not, then who cares if there are staples in them............ you still see the wood edges and that's the important part of the wood stair/runner look.
If you remove the original ring shank nails from the tack strip, you can use smooth wire nails to hold the tackstrip in place.......... they would come out cleaner if you for some reason decide to go back to bare wood. I have gone as far as slightly pre-drilling the tackstrip and wood tread and screwing the strip down with drywall screws............ the screws + pre-drilling would make future removal a breeze and the pre-drilling would make filling the holes a breeze since there would be very little tread damage.......... just some nice clean holes.
One more thing.......... Say the stairs have a runner on them for 5 or 10 years, then you want to go back to bare wood. The treads under the carpet will be discolored since they will have barely seen the light of day. Only the exposed edges will have seen daylight, interior lighting and occasional cleaning. That will change the color of the wood at least a little, if not a lot on the exposed parts of the tread. If there was any glue, or double faced tape used when trying to use less fasteners, the stairs will require a total refinishing anyway. Was there any real gain?
How about this.
Remove the nails from the tackstrip and using an electric carpet tacker, tack the tackstrip in place at whatever distance you want from the riser. Just use one or two electric tacker staples just to hold it in place. Next, pre-drill 4 holes through each tacktrip and into the tread. Screw the strip down with short drywall type screws. They make plated screws that are gold colored if you are concerned about rust or discoloration. Use a drill bit that is barely narrower than the screw diameter. This will leave a clean hole in the tread that will be easy to fill if it was ever deemed necessary. You'd get no splintering from this method as you would get from pulling out the original tackstrip nails..... no pry bar needed with screws either.
Duofast makes staples shorter than 9/16.............. I think close to 3/8, which might provide decent holding power in the riser to hold down any minor puckers without overkill. Under the nose tho, depending on the carpet of choice, you would most likely still need the 9/16.
Fastening the pad can be done by duct taping the pad to the strip, then duct taping the nose edge of the pad to the under side of the tread. The duct tape adhesive will harden over time and most likely will not be removed without solvents and or, a scraper. Double faced tape could be a nightmare to remove, with most being a bit gummy.
Basically, if you are going to carpet the stairs................ you can't really have it both ways.
15 years later, no matter the runner installation method you would more than likely, need at the very least, some light sanding and a new coat or two of finish to blend any discoloration or minor scuffing and side wear. Is filling electric tacker holes going to be that much additional effort. Give it some thought as to if you would ever want the stairs bare again.
