Whether 50k is worth it or not depends on your travel patterns and what you hope to achieve by being higher up in Aeroplan's pecking order.

As others have noted, if your primary interest is upgrading on international flights, well, don't get your hopes up. The SEs and 75ks will still beat you to any available seats that do come available and, even if you do manage to score one, remember it will cost you a few hundred bucks in co-pay charges in addition to your e-credits. Is that worth the expense of a short MR to you?

If your interest is in upgrading on your domestic travel, then 50k might be worthwhile to you. Ditto for booking any Aeroplan reward flights, as (in theory at least) you'll have greater availability to choose from than a 35k. But even if you stay with 35k you'll still keep domestic lounge access and priority boarding (which can sometimes represent about half the passengers on a given flight).

If you do elect to do the short MR, I encourage you to keep it on the cheap because the benefits of being 50k over 35k are not exactly earth-shattering. Look for deals on ITA ... US Air is presently offering YOW-PHL-BWA-PHL-YOW same-day turns for $358 for the week of Dec. 9. If you're already earning the 500 mile minimums, that's an easy 2,000 miles.

AC may gift you the 50k anyway, being as close as you are. But maybe not. If you can articulate clear, specific and realistic reasons to attain 50k, then you may want to spend an extra afternoon in the air to guarantee it.