Merge mining can indeed become parasitic, at least psychologically. There's a solution for this Myriad has been working on called Mutli vPoW. Instead of only using one auxPoW algorithm, as is the case presently w/ Syscoin, there are multiple PoW algos and only some of them are merge minable. The algorithms that are merged mine have smaller block rewards (called block tips) than the algorithms that can't be merged mined. This helps create a better balance and prevents some of the downward pressure.

Here's a more in-depth write up: http://myriadplatform.org/multi-vpow/

Myriad's also now merge mining Syscoin on all of its scrypt p2pools. I've been holding my mined Syscoins. I like what I see so far. I've been advocating a lot of these features to be implemented in Myriadcoin's network by way of merge mined sidechains.