Just one weeny point. You say that you have never used your IR for airways work apart from your IR training/test. Why not?
Like yours did recently, my I.R. cost me a relative arm and a leg when I got it and I can remember getting back to my Midlands home airfield, newly issued rating in licence, finding a friend, bunging him in the RHS of a full airways C172 and steaming off on a flightplanned round robin. As I passed FL45 on the climb into the daventry control area I can remember claiming "over 4500 feet and I am LEGAL!!" Then it was up the airway, an approach and ILS for a go-around at EGBB and radar vectors for an NDB back home. I was in a rented C172 and had joined the big boys for a while! Yes I added the hire cost onto my bank loan but boy, it was worth it!
P.P.
P.S. My I.R. cost me three grand, so it was some time ago!