mastering inverted flight shouldn't be the limiting factor to advance to the next level of aerobatic plane,but being confident and doing the basic manuevers smoothly is a indicator that your ready for the next step.
I have been back at it for several years now and still feel uncomfortable with inverted flight,mabee its because I didn't practice the basics enough[X(].
moving on is a personal thing,a good second plane is a 4*,or a Sig Somthing extra also a good kit to work on,I chose a fun kit called a GIZMO.
if you want to try a more manueverable plane ask a more expierenced club member to help you out to get it up there, and give it a try,its what I did and found out it wasn't that hard after all.
I was given the oportunity to fly a fellow club members plane,a U Can Do,and I knew I was ready for the next step after flying his.
when I built my second plane the GIZMO,I had a club member trim it for me and I didn't fly my trainer again,again with some help from my club members I have been flying warbirds which is my main interest in RC,really do what you feel is right.
best wishes for your wife also,I don't know what I would do without mine.