I read somewhere before that commonality does save money in AE but is there a way to see the savings?
Look at your "maintenance costs" link under the finance page. It shows the base cost of each type you operate, plus the cost for each aircraft in that series. For instance, My airline operates ERJ-145, A319, and A320s. There is a base cost for the A32x series and a base cost for the ERJ series. Under those headings, there's a cost to maintain each aircraft. The A319, for example, is slightly cheaper to maintain than the A320, but there is no additional base cost. As you add more of a certain fleet type, the base cost is spread out among more planes, helping your costs.
I probably wouldn't play, just because school is starting up in a few weeks and I'm already running 4 airlines on three sims. I think it's a good idea, though.