Rods, reels, line, lures, electronics, motors, maybe a new boat?
The minimum boat to be on any water at any time in Colorado is a 12 to 16-foot deep-V with about a 25hp outboard. Even at a small lake like Chatfield the wind comes up quick and I won't even start to mention Spinney. There is a reason most Canadian outfitters supply a Lund WC-16 with a Mercury 4-stroke: because they work great. This boat will troll, cast, rig, and jig just fine with a small 55-lb electric. If you have this, move on and spend your resources elsewhere. You may want a bigger rig but truthfully, this simple boat will work 90+% of the time and cost 90% less.
For sonar, vertical pixels matter. If you have a handheld GPS then anything with 640 vertical pixels will show as many fish as a larger and more expensive unit. The Humminbird 571 HD DI fits that bill for $250 retail. Add GPS for $50 more with the 581i HD DI Combo. The 688ci HD Combo adds color. I tell people to invest in side scan if they are detail-oriented, enjoy mapping, and enjoy working with electronics, otherwise, you will probably never realize its true potential. Larger units help if you have multiple people watching sonar at once. Effective sonar does not need to be expensive and if you can find fish you can catch fish. Most anglers end up using 2D sonar 80% of the time and switching to downscan or sidescan to verify 2D readings.
My next recommendation is always a guide trip. If you share the boat $150 or so gets you in-touch with seasonal patterns and traditional lures for your favorite lake. This will save you time, money, and is a fun day. A "masters class" of 3 to 4 trips will cover each season for walleye: Spring night trolling, Early Summer Rigging and Jigging, Trolling for suspended giants, and fall spooning and long lining are the skills you need to fish year-around on Metro lakes. A short ice fishing trip will round out your skills too. These trips and time on the water are a great step forward for any angler.
Once you know the 7 lures needed for your lake buy 3 of each of the 3 best colors. This will add up to about 64 lures. For Chatfield that's 9 Husky Jerks, three bags of Gulp! Minnows, Some #8 octopus hooks, 9 PK Spoons, 9 Blade Baits, 9 Shad Raps, and 9 Jigging Raps for ice. Add in some deep husky jerks for Cherry Creek and Pueblo and maybe a nice set of spinner blades from JT Custom Tackle if you are branching out and visiting multiple lakes. Of course you can always use a few more here and there but again, this is really all you need.
If you do not have a set of 4 or 6 trolling rods with line counter reels (I suggest the 7'10" Fenwick Eagle GT telescopic with Abu Garcia 6500LC reels), a 3000-yard spool of Trilene XT, and planer boards, this is your next big purchase. A matched set makes trolling a dream while mixed reels, lines, and boards, eliminates many of the advantages of trolling. Sell your old stuff on ebay and match everything up this winter.
Rods trickle down to the end of the list but if I was forced to use the rods I grew up with (random $20 fiberglass combos) I would not be as happy on the water. The reason I like Fenwick is because the HMX rods work great, and anything higher (HMG, Elite Tech, Aetos) all work better. I use medium action rods earlier the season (rigging and jigging) and medium-heavy rods in the fall slab spooning and blade baits. Also, a nice jigging rod can go a long way to enjoying the sport.
Now that I think about it, most reels these days are pretty good. Stick with the main brands and you will not go too far off. I like reels with extra spools like Pfleuger, Wright and McGill, and Abu Garcia.
The last thing on the list is a spool of Berkley Nanofil in 10-lb test. I really have enjoyed using this stuff this year as it casts further and has better sensivitity than braid and is fun to use.
If you have all of the above then consider yourself pretty lucky and simply try to get more time on the water. I learn something from every trip and getting out is the main part of the battle.
There you go, a shopping list for the winter and a true sounding board for what you need vs what you want.