Aren't the latest f-16's also mainly 2 seaters like f-16i/f-16f/plus isn't the su-30 a 2 seater india's version of the pak-fa will be a 2 seater.Also take a look at the different variants of f-15e's they are all 2 seaters .maybe in the air superiority role a single seater is ok but for strike missions i still think a 2 seater is more desirable
Back in the late 70's early 80's a Phantom pilot of note who's name I shamefacedly admit I cannot now recall said "Replace my RIO with a machine? Hell, yeah, when I can shout "switch to Winders" and the machine can do that..."
We're at that point and beyond.
So, simple question - you're doing deep strike and interdiction. Guy in back or say, another 500 lbs of fuel? That's what that person in the back (or "Hostage number 2") represents, once you've added the weight of the ejection seat and sundries to his own weight.
With direct reference to the question, should we buy more Typhoon, my answer would be "No" - F35 will be a bit cheaper, a lot more capable and still have a large UK workshare.
Funding a twin seat strike version of Tiffy? No thanks. Cockpit automation has reached the situation where even in the Tornado, 80% of the mission could be flown from the front seat and in the case of Typhoon, the navigation, weapons release and countermeasures are all well within the realms of modern computing standards.
Better yet, buy F35 and just have a quieter life with less people shooting at you (if they can't see you and you have a much better chance of seeing them first, it's easier to conduct and prosecute strike missions)