I would love to have a TD-10 with expansion capabilities. This would be a great tool to use. My current projects wouldn't call for it, but I could put it to use in the future.
At the time I got my SPD-20, owning a full-blown e-kit was not even a thought in my mind. Now it is going to soon become a necessity.
When I was recently and briefly in drum sales, I would tell people to
"consider their future needs before they make purchases" as I would direct them to the TD-10.
This consideration is something I hadn't done in the past.
For the studio projects I've signed to, I don't even use the sounds in my SPD-20. I just use the VST plugins in Cubase. Make the drum tracks/loops and email to the producer.
He does his own tweaking to suit, and then the PayPal is in the bank!
This is but a precursor of things to come. I'd better save up my pennies and prepare for the future!
I guess my best advice is the advice I didn't follow a few years back.

As you weigh the benefits of the 8 and 10, consider your future pursuits.