Walkingthewalk,
I`ve met a lot of instructors who have, quite mistakenly, made the same assuption as you.
Upgrading to FI (having observed 25 solo flights) is one thing but it does NOT make you a QFI. Your not a QFI until you have had the "no applied instrument" restriction removed from your instructor rating!
Getting back to your question, I do think you should get some sort of payrise.
Your employers may say that you are not entitled to a payrise until you can teach the IMC rating (ie. by becoming a QFI)
The privilages of the FI(R) and FI are not really significantly different. If I remember correctly the only things an FI can do which a FI(R) can't is send first solo's and work unsupervised. Is this really going to put more money into your employers till?
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Pull back and the houses get smaller - pull back a bit more and the houses get bigger!