I know Geronimoo isn't doing a lot of work updating the simulator at the moment but I'll still put forward three substantial requests. Maybe someone can help him out.
Firstly it would be good to have some "user values" that could be defined at the start of the script and calculated from existing terms in the simulator. For example you could define a user value as "Count in deck: copper" + "Count in deck: curses" and then reference that user value in the purchase conditions. This would allow the user to create far more interesting purchase conditions without great changes to way the simulator works. The user definitions could perhaps be on another tab at the top of the script.
Similarly, it would be good to have a purchase/gain condition of "When playing <card name> with <card name>". This would allow the user to take many of the most difficult decisions away from simulator logic. So as an example, if you could specify a line of Buy Gold when playing Mine with Loan then the simulator would check the buy condition to see if you were playing a mine, if you had a loan in hand, and then gain the gold by trashing the loan. Existing purchasing logic would continue otherwise.
I imagine this second request would be a heck of a lot more work to code but would let users themselves solve problems with mine, mint, remodel, upgrade, develop, expand, horns of plenty, ill gotten gains, ironworks, workshops, universities, thief, etc. The simulator wouldn't need increasingly complex AI to deal with each situation. It also fixes a variety if logic problems where you want to gain card Y by trashing card X and you can't do the same tests before/after card X is trashed.
Thirdly it would be good after a simulation to keep a record of the final decks, something like the average number of each card type for each player. It would be even better if there were separate records for winning decks and losing decks. This would let the user find out more easily whether the kingdom cards are being bought and whether they have any impact. Maybe this data could be presented on a new display window. The simulator certainly doesn't need this feature but it might be nice to have.