The Rose Primer:
To get the best possible flowers, cultivate the healthiest rose. As I'm organic gardener, I keep 4" of organic mulch--hay, in my case, but there are many possibilities--on the ground under and around the rose, water if the weather gets really dry (no rain for a month), and prune according to the kind of rose. The mulch is a good idea in any case, to moderate the temperature of the soil and retain water, but there are probably other satisfactory methods to feed your rose.
Roses need sun--some more than others--water, ditto, though they tend not to be thirsty plants. They need good ground, a five dollar hole for a fifty cent plant, as the saying goes, dug when the plant goes in; no amount of fertilizer afterward will compensate for no decent ground to grow in. They need not to be in ferocious competition with the roots of trees or other big plants, or choked by terrible weeds (again, mulch is helpful in deterring weeds).
Well cultivated roses are more resistant to diseases and insects than ones that are poorly cared for. Then, some varieties are more disease resistant than others. As far as your bugs are concerned, look at your general methods of cultivation. If you're taking good care of your rose, and it looks generally healthy, squash as many bugs as you can find, encourage the presence of bug-eating birds and animals, and don't worry about a certain amount of gnawing.
About the weak stems, that may just be part of the basic character of the rose, like a person's being short or having red hair, and if that's the case there's not much you can do about it. Roses also differ in their pruning needs, although if your pruning were drastically wrong probably you'd never see any roses at all. If your rose is grafted, not grown from a cutting (most roses in commerce are grafted), at nine years of age it may be getting old and losing vigor (though I'm not sure about that). About the full-petaled and few-petaled blooms, I've seen some of my roses produce decidedly fuller and larger flowers when they were in particularly good shape.

This is basically a sketch of how I grow (and have always grown) roses, organically. It works for me; I don't know how adaptable it is to your situation, or whether any single bits of the advice here will correct your rose's problems. You might find it worth your while to check out the forum on Roses (mostly US, as opposed to this European forum) and the one on Antique/Old Garden Roses (OGRs), which have a lot of discussion on rose cultivation--and a LOT of gardeners in your part of the USA.
Good luck! Melissa