Painting stairs- carpet runner

[yawningbear]

Currently we have a very dirty looking like (despite lots of cleaning) carpet up the stairs. I have had a look underneath and it looks like previously there had been a carpet runner with edges at least painted. I want to replace the full stair carpet with a new runner and re-paint stair edges to freshen it up.

As they are already painted, is it just a case of sanding down (and could this be done by hand, with sandpaper as opposed to a sanding machine) and putting on a top coat of floor paint? If so this seems do-able to me, but I don't want to rip up the existing carpet and create a whole lot more work for myself as I am time limited & cash poor

There was a thread on here a while ago about whether to have a runner or not and lots of people came on to say don't. I'm on the fence because we've recently got one and I think it looks fab. But...The down side is that the lovely painted white bits on either side gather a lot of dust and need a quick whip over with a duster every day to look good. Needless to say, this happened every day for the first week and not since.

I just used the eggshell that we used for the banisters, because it doesn't get direct wear. However, I have had some problems with it cracking in the corners where the stairs flex, so would be interested to hear what others have done. Prep just as for any other woodwork.