Nice to see a sensible thread!
Although SEP flying might not be the most relevant type of flying for an aspiring airline pilot hours in your log book show commitment and that you have sustained your interest. Airlines still prefer the candidate that loves flying.
There may be some value in occasional trips in a sim where with a good instructor you can push yourself to develop your IF skills and perhaps share the cost with a flying buddy.
It's a shame but it seems true that the FI market is saturated and aerial work jobs are as rare as hens teeth, that said there are cheeky opportunities here and there as safety pilots in king airs etc which may be better for networking than keeping current.
I'm sure nobody needs to be told to keep applying left right and centre to every single operator every few months with a covering letter, CV and perhaps a copy of your final flying report from your FTO (can make the difference).
Hang in there boys it will happen.