If all else fails, and your're willing to take the risk of a small discoloration in lieu of the large dent. I have not done this on a dust cap, but I have used this technique with 100% success in other applications. There's no reason it shouldn't work - but use your own judgement based on the dust cap material and stiffness. Also - it's very likely that even if you pull the dent out, there will be light "wrinkles" remaining in the cap that are impossible to remove:
With the speaker on it's back, drivers facing up,
1. Place a dab of "5 minute" epoxy (NOT superglue!) on the head of a light construction nail. Make sure to "wrap" the epoxy around the top of the head AND the behind the head so that once the glue cures it surrounds the entire head in a ball. The reason for this is you will be sticking it to the cap's dent, and then using it to pull the dent out - you don't want the nail to pull off and leave the glue on the dust cap.
2. Allow the glue to cure enough so that it is still sticky but formed enough that when you hold the nail head (very lightly) onto the center of the indentation in the dustcover it won't run. This also ensures enough holding power after cure, but not TOO much. You don't want it stuck on there like you're planning on towing a boat with it :)
3. Place the sticky nail into the center of the dent, and hold it there for a couple of minutes - until the glue has cured a little more. If the speaker is placed on it's back, you should be able to "balance" the nail there so you don't have to physically hold it for the next 10 minutes.
4. When the glue has cured enough (probably about 15 minutes after mix - not to rock hard), carefully pull the dent out and place the speaker back in it's normal upright position.
5. The nail and glue are removed by heating the middle or even opposite end of the nail with a cigarette lighter or candle until the whole nail gets hot enough that the glue on the end becomes very soft. It should then just pop or peel off pretty easily. (Now you can see why you want the glue "balled" around the head.)
6. Any trace amount of glue left on the cap should be removed with Goo Gone, Goof Off, or acetone, etc. IMMEDIATELY - but test the cap for "colorfastness" first in a very small spot.
I would recommend practicing this technique once or twice on something else to get your timing down beforehand.
Hope this helps - or at least provides fodd for thought.
