As it seems we're commited to paying for them all even if we don't get them all, it seem daft to me to say we don't want them because we can't make a saving on them.
So why don't we take delivery of them all? Then put all the a/c into a continual upgrade/operational/storage etc etc cycle?
This would give the operators the most upto date airframes available.
Flying hours could be kept low helping manage FI so that the a/c could be operated nearer to its full RTS for much longer.
Additionaly by managing the fleet properly the useful service life could be extended by many years providing savings in the long run.
As for it's role. The F15 was designed as an air superiority fighter "Not a pound for ground" was the quote I seem to remember. It seems to be a decent enough ground attack platform now. (Please correct me if I'm wrong)
Writing off Typhoon as a ground attack a/c so soon seems premature to me.