For fun I took a look which pool confirmed the about 7000 blocks which contain about 14000 Mastercoin transactions and it turns out Eligius confirmed only 6 blocks of them which is far less than the expected value given the portion of total network contribution.
So I was wondering.. are you actively blocking Mastercoin transactions?

Yes, the spam filters are capable of picking up most Mastercoin spam.
Please don't play games to force us to upgrade it.
Hopefully more pools will gradually improve their spam filters too.
What you call 'games' we call 'resistance to censorship, and is definitely on our roadmap.