Allowing them to use the advanced version of the basic moves sounds cool! I must admit nobody has taken them in my home campaign yet, so there is also an incentive for me to see dice used for that :-) [Although someone might pick them up before the Nationals, my players' current curiosity is more in the direction of trying different playbooks. Kinda everybody has either taken moves from a second play book, cast eyes on making a second character or replaced their starting character…] I also like that that gives a function to the physical dice they bought.
Some way of giving access to other moves players don't have yet sounds fine.
If I remember correctly, I read a report of someone GMing Dungeon World at a con, allowing players to spend XP for using advanced moves. So a one-off use of a Playbook move you don't have, similar to the suggestion for using Advanced Basic Boves, sounds good. Also I probably should come up with some setting-flexible advanced moves or move templates anyway, to show off what the system can do.
I'm a bit skeptical about buying advancements, that sounds quite cheap. But seeing the DW example in comparison again, maybe buying XP (i.e. 5£ per advancement, somewhat less cheap) might be appropriate. What do people think?