I hear you on the warm/neutral/cool issue...I am pale and warm-toned (pale olive) but with more gray/blue in my dark blonde hair these days. One eye amber, one eye green. Always done better in silver jewelry than gold, generally really bad in blue-based lipsticks (which most are). I find it quite challenging sometimes to negotiate the warm/cool divide. But, speaking of shadow palettes, I inadvertently covered the issue last year by picking up both cool (denimy blues) and warm (goldeny browns) eyeshadow palettes from Wet 'n' Wild that I alternate with brown and blue eyeglass frames (e.g., the bluey shadows with the brown frames) in most everyday applications. I have a decent-size collection of makeup already, but much of it tends to get used as occasional accent, whereas the basic neutral tones (denim/brown/gray) are where I go for everyday wear. Wet 'n' Wild is one of those dirt-cheap but quite high-quality drugstore brands, so, great for experimenting with, and spending extra money isn't really a problem.
To answer the question, though--each year I might add a few shadows in colors I don't already have (usually palettes as they're more bang for the buck, save space, and are great for travel), maybe an eyeliner or two in fun colors (possibly a colored mascara as well), and a few lipsticks to add finer distinctions to my collection of warm tones (my faves: Revlon and M.A.C. Latest buy: M.A.C "La Vie en Rouge"--which is a warm, dark pink, ironically). I go through foundation slowly (good, because it's really hard to find the right pale-enough and yellow-enough-but-not-orange combo), so that's not a frequent buy. Same with concealer, which I use but slowly. I think mascara might be the most frequently replaced thing (I use Cover Girl LashBlast. I figure that $7 mascara looks exactly the same as $20 mascara.) Oh, wait, also powder--I do go through a compact of that every year (again, cheap--Cover Girl and Wet 'n' Wild have some that work for me). I forgo blush even though I'd probably look better with it...my skin has never tolerated it. You don't even want to know how old my fave eyebrow pencil is...I wish Guerlain still made that color.
What has changed majorly for me in the past 10 years: skin care. Very few commercial products and all very economical. I take off makeup/cleanse with extra-virgin olive oil. A Paula's Choice AHA (day) and BHA (night), which last me more than a year each. Oil of Olay knockoff from Trader Joe's at $4 is my day moisturizer/sunscreen, lasts me quite a while. Night moisturizer when I feel I need it: a couple of tablespoons of coconut oil mixed with a couple of drops of EVOO for pliabilty, kept in a cosmetic jar thingy I got at the drugstore. I don't really buy big in skincare, so I figure I can play a little in the makeup area but I still keep it pretty unspendy.