Divide them up - they won't take up nearly as much room & you can get rid of the old, the extras & the ones you don't need. You don't want to plant whole clumps next year anyway so divide now & save yourself the trouble next spring when it's planting time.
Look at the answer jroot gave to the question about the big clump so you can see what you need to do.

Why is it you can't plant the whole clump?
I have enough space, just had a new area plowed this year that I am going to use for nightshade plants and cutting flowers.

The reason you divide dahlia clumps each year- or at the least every other year is because the bigger the clump the less vigor the dahlia plant will have. A plant's mission in life is to reproduce & if it has a great big clump of tubers to live off of it won't try as hard to put out blooms. The stems will get weak & floppy & you'll get way less blooms. You are better off with a nice healthy tuber that puts out one nice fat sturdy stem with many laterals than you are with a spindly plant with a lot of stems that are all weak. Also- the size of the tuber doesn't really matter- a small one puts out just as nice a plant as a huge one does. Look at our photo albums- each one of these plants is grown from a single tuber- notice the vigor & the amount of branching from just one bigger-than-a-broomsitck stalk

Here is a link that might be useful: photos of dahlias