From the terminal (and the terrace) you miss what's using the new runway as I suspect you know.
What I can't tell you is whether arrivals in T1 even see a useful window. Arriving in T2 you don't.
There is a bus to the eastern end of the original two runways (nr Zeppelinheim) and there is surely still a pub or two in that village. (two buses to get there, one to get back IIRC, also trains, change at Sportfeld)
I used to walk frequently from T1 to the eastern end, and occasionally to the western end which is a bit far.
My opinion is that - as long as visibility is adequate - the ends of the original two runways are the very best spotting spots and although I'm no photographer, likely best for pictures because the sun is mostly behind you. I'd be very sad to take a trip to a foreign airport only to notice that all the best stuff is somewhere invisible. If all else fails, take a taxi or hire a push-bike to get to the best viewing point.