I love that I always learn something on this site. The you look fab website looks like a great resource for me too! So, I'm a pretty hip dresser (my friends ask me to help them) and I'm about your age. First I'd suggest figuring out what your body shape is now. You are probably dressing your shape as of a few years ago. I notice that a lot of the time people who aren't happy with their clothes are picking the wrong shapes or trying to add in a trend that doesn't work for them. My two best shopping friends both have opposite shapes from me. I'm straight (or waistless, as I call it) with a big top; they are curvy (hips, waist, top) and hippy (slim top and waist, big bottom). Shopping with them is hugely helpful because I can see exactly why something that I love isn't working on me. When something doesn't work, it looks dumpy, even if it is expensive or hip. You can pick up a lot of silhouette tips from What Not to Wear. If you don't get cable, check out their website. Once you know what shapes are easy for you to wear, you can buy those shapes and you'll be a lot happier.
I like to buy trendy clothes at affordable stores like Target, H&M, Old Navy and Ann Taylor Loft. I spend more money on basics and buy them from better stores or from discount chains carrying more expensive brands. A $40 pair of pants that started out at $200 are made a lot better than a pair that started out at $40. I buy basics on sale when I can. All pretty standard advice, right?
The key to remember is that the stuff you didn't spend a lot on is going to look bad, worn-out, dated, etc., sooner than the higher quality stuff you bought. I have lots of tops from Old Navy that work for a season, but then look dreadful. I give them to Goodwill. I have ten year old tees from Banana Republic (their sales are killer, by the way) that look great even today.
You said you have things that are newer and in good condition. Wear the outfit to a store like Ann Taylor Loft and ask them to suggest an accessory to update it or a new piece that you can substitute for part of the outfit to update it. They should be a great help.
Good luck!