The cost of track covers would be equivelent to 1 rain off or less and you will save on average 5 meetings per season with them, you just need around 8 volunteers to cover the track at somepoint before rain starts and some people who are in the pits before the meeting to take them off, preferably start around an hour and a half before scheduled start time, obviously dont take them off if it's still raining, that gives time for the track staff to work on the track.
It attracts the riders though... fact, wether you are paying your riders more or not it attracts riders to the club because of the money being put into it. Take Dan Bewley, was riding for Edinburgh (a very siccessful team) and moved to Glasgow despite surely being wanted to be retained by Edinburgh.