No need to be sorry Viv, you've put in a HUUUUUUUUUUUUUUUUUGE number of units to a worthy cause. I only have crunching running on 1 PC (and it just runs when there are spare CPU cycles)
Hear hear to all that the others have said. You will still be making a very valuable contribution to the overall cause. Taking part is the important thing, regardless of whether one crunches for just an hour or two per day, or more; and of whether one rig is crunching, or several.