I don't really think a young cat needs to be seen twice a year, unless there are other health issues requiring more frequent monitoring. As for seniors, I don't think twice yearly exams (along with bloodwork at least once a year) are overkill.
To be quite honest, I like the vet to get a look at my cats (and the once-a-year Purevax rabies vaccine requires it), but without bloodwork and further diagnostics, I can't say that you're neglecting your cat if you don't take them in for check-ups. An observant owner is going to notice most obvious (as in, outwardly visible) issues, anyway.
I have had kitties live to be in their twenties with minimal care, so it can obviously be done differently. I often wonder if I'd done all sorts of diagnostics on Sam, if I would have been freaking out about CRF for many years before she finally became ill and died at 22. She was never sickly (until the very end), so who knows if it would have been worth it to go nuts over her bloodwork?