You being a seasoned IFR-pilot, how large a percentage of your IFR-flights would have been cancelled entirely and how many would have seen you diverting to your alternate, given the restricted nature of the EIR?
Simple question, very long answer, potentially.
I normally cancel a flight if there is any real prospect of diverting, because on the flights I do there is generally no point in ending up at the alternate (and some don't even have avgas).
My despatch rate on the holiday type flights is about 75% to get away from the UK, increasing to about 95% when we allow a 3-day slot i.e. I have 2 more days to play with.
The EIR would reduce the 75% to perhaps 50%, not because the wx at the destination is bad enough but because I would simply not go in the first place if an instrument approach at the destination was a no-no. But very much depends on where one is going. If going to a coastal destination, with the right kind of airspace around it, one has a lot more options if one is "clever" about it. But I am not really sure. I wouldn't bother with it; I would go for the full IR which will be only a bit more effort. Cancelling IFR at a high altitude, in some places, is a recipe for hassle at best and for killing oneself (or just creating hassle for ATC because one gets pushed into a DIY letdown) at worst.
A very common situation is FEW or SCT with a base of say 3000ft, but the IFR-cancel option which will be mandatory with the EIR tends to not be available that low down. So, I think the EIR will primarily benefit pilots who are "clever" and who know how to work the system - basically what I used to do before I got the FAA IR in 2006.
It is a fact that most IFR flights are done mostly or wholly in VMC but there is a completely separate question whether one would embark on them in the first place if the fully-IFR option was not available, because the FEW or CAVOK conditions needed for an assured legal-VFR descent from the high altitude enroute segment can be totally relied on on only a small % of flights.