So instead of buying cheaper accessories and eventually replacing them later with better quality ones, I am planning to buy better quality ones and only exchange/upgrade the body.
Do you guys think this is a good strategy? If not, what would be a better one?
I think the best strategy is to constantly re-evaluate what your needs are, what the marketplace offers, and where you might go in the future. And to purchase only what you need; not just what you think you want. That could be something completely unforeseen, like the advent or mirrorless enticing you away from dSLRs to other systems and having to sell all your glass/bodies. At this point, maybe only your support gear and manual off-camera flashes aren't going to need a swap. :)
Full frame is a sidegrade, not an upgrade. And it's hideously expensive, because all your lenses change character and many of them may not work any more. But the advice to "only buy full frame lenses" really sucks if what you need on a crop body now is an ultrawide zoom. Any full frame "ultrawide" (like the 17-40L) is basically just walkaround on an APS-C camera. Better to get what you need now (10-18, 10-22, Tokina 11-16) and then sell it on when you actually do make the move to FF, rather than using a not-quite-right lens for however many years it takes.
But I would also say that you need to evaluate if what you think you want is because you really need the thing, or if maybe lack of technique/knowledge/experience might be the real issue. Some folks think they need VR, when all they need to do is learn how to hold the camera properly and what shutter speeds are good for handholding. Some folks think they need a faster lens, when a tripod or flash might do a better job of solving a not-enough-light issue. Some folks think they need full frame, when shooting in RAW and simple post-processing skillz may need to be acquired. Or at least to learn not to underexpose and push in post. Some folks think they need a far more sophisticated AF system, when maybe they just need to learn how to set up back-button AF or how to use the different AF modes/zones/points.
Make sure it's a hardware limit that you're pushing against, and that the gear you want will actually solve that problem for you. And maybe risk a bit of budget on a rental to grasp the reality, away from the dpreview messageboard discussion reality-warping effects are.
I own three L lenses. I can tell you categorically that one's first L lens is going to hit you with the hardest case of buyer's remorse you've ever had, simply because the multiplication on pricetag isn't really equaled by a similar multiplication of performance. A lens is still made of glass and that glass still obeys the laws of physics/optics. And bad technique follows you, no matter what gear you own.