I changed my MDX spark plugs out at 75,000 miles and I'm almost due for my 105,000 service my next oil change. The early spark plug change will save me a little money during that high dollar service. I waited until the 105K service to do my plugs on my TSX and RDX a few years ago (both due around the same time). After the new plugs, both vehicles had faster starts, a little better acceleration, back to normal mpgs, and felt like I got back a few lost hp/tq on the old butt dyno. I didn't want to wait until 105K service on the MDX since the big girl is a little bit more sensitive about power and mpgs.
Some folks sometimes found a loose spark plugs from the factory and drove the MDX for years like that with sometimes scorching on outside area of the plug. Changing now would be a good double-check for this.