I actually find q-tips dipped in ETOH to be fairly useful at getting rid of all the crud that has accumulated on my coil as well. I scrub at it, then q-tip it, then dry burn it. It's totally normal for coils to get gunked up, but as long as it's glowing well and there are no hot spots after whatever method of cleaning (I clean my coils as they are largely SS, and so I pulse them more than just dry burning the heck out of them to clean them, as they last longer that way) you should be okay.
I find my coils last pretty well using this method. I use rayon, so my coils don't gunk up quite as fast (although I don't use highly sweetened juice usually either but I do have *some* gunking factors) and that's nice for me in terms of time.
Unless you are really fretting, if you like your juice, you don't need to change it if you are alright with the amount of re-wicking you are doing. Rayon does last slightly longer than cotton, and I just straight up prefer it, so I mention that, as I do, LOL.
Anna