What do the docs say? if not, you can post an Idea.
I was wondering if there are any that allow you to identify if someone engaged with X amount of RTP Recommendations?
^^Yes you can. The constraint is called "Min. Number of Times". This constraint is available on many filters/triggers.
What about determining if their engagement with RTP Recommendations is trending up or down based on a calculation of their average weekly or monthly engagement?
^^Most likely No. Marketo does not do any calculations. You can get fancy with filters and only accomplish so many things.