Didn't hear of your for quite a while... If you have the time, please visit us at IRC channel #dylan, on irc.freenode.net. I'm sure we have much to discuss.
But yes, implementing infix macros by adding rules to the grammar is a thought that has crossed my mind. This would be much more straightforward to implement, and give better error reporting.
In case you haven't seen it yet, take a look at Peter Housel's Monday project (http://monday.sf.net). It contains a nice extensible parser framework.