I agree buying HP merch feels subversive. I recently bought a bunch of HP merch when it was in the Aisle of Impulsive Purchases at Aldi. Sadly both DCs are over their HP phase but I most definitely am not.
I used to keep my love of HP under wraps a bit - I'm nearly 40, I have an English Literature degree, I should probably be a bit more highbrow - but now I positively delight in buying HP merchandise. Every time I buy something I think 'royalties!' and I while I know it barely even counts as a drop in the ocean, I want to do my bit to ensure anyone looking at the bottom line of comments out vs money in sees that JKR is not losing that game. My house is filling up with the stuff!
Which reminds me - the new illustrated (Jim Kay) edition of The Order of the Phoenix is out later this year, pre-orders now available!