While I agree that the system can be exploited, as a GM I'd just slap some penalties on a player trying to do contacts + monocles + glasses + goggles, say, oh, I don't know, equal to the bonus he would get...
Now, that's if the player went all out (and lets face it, some of them do); I think there are several viable options.
First of all, since "everything is wireless!!!111!11!one", it is not too unreasonable to think that some of these devices could interact with each other, as opposed to being "layer upon layer" of optics. Given this train of thought, consider the following:
1. Vision Enhancement "sharpens a character’s vision at all ranges"
2. Low-light and Thermographic Vision "allows you to see normally in light levels as low as starlight" and "enables vision in the infrared spectrum", respectively
3. Flare compensation "protects you from blinding flashes of light as well as simple glare"
4. Vision Magnification "digitally magnifies vision by up to fifty times"
5. Image Link "lets you display visual information in your field of vision" and "is what you need to truly "see" AR"
Now, with all of the above, and considering that devices can wirelessly interact, is it really that hard to imagine that a pair of contacts with vision enhancement, glasses/goggles with low-light, thermographic, and flare compensation, and an implanted image link can provide all benefits normally?
I'd say the one exception to this is using thermographic and low-light simultaneously, as they provide different bonuses and have different uses (low light vs total darkness).
That all being said, you can put ALL of the vision enhancements available in rating 4 cybereyes and supposedly get all the benefits, so why exactly is it that some of you think that somehow these devices would not be able to interact with each other if they were layered differently? Any discussion at this point is about fluff, as I see it, as the rules clearly allow you to have some vision enhancements implanted, some installed in gear, but fail to provide guidelines for what stacks...