For those of you who might not be familiar with the concept, Bitcoin Days Destroyed is an interesting metric for transactions. For every input, you multiply the coin age (when the transaction was included in a block) by the amount of coins being spent. You add up all of the results for the whole transaction Nd you get your BDDs. So, spending 1BTC a day after it was received gives you 1BDD. A week after it was received - 7BDD. 0.1BTC after a year has 36.5BDD and so on.
Now, if the order transactions are priorities for inclusion in a block was dependent on their BDDs as well as fees and size, it could limit the effectiveness of the spam attack - since the spammer relies on sending a lot of transactions often, unless they have a lot of coins, their transactions will have a very low BDD score. Standard users should have higher scores by default, provided they don't cycle their coins all the time.
Of course, this method only works if the mining pools would follow the rules. Seeing how many pools still mine blocks that aren't full gives one little hope the situation will be resolved quickly.
Side note - this solution isn't all that new either. I did write it down broad strokes in my master thesis (pages 42-43) back in 2011-2012 ;).