I'm thinking about possible upgrades to my Surly Cross-Check. It's good enough for a tour as is, but I can spare some for my commuter/touring bike. Here are some things I've been considering. The upgrades are kind of pricey, but I can do it slowly over 6 months. You can skip to the bottom where I have the real question about long/medium cage derailleurs and mountain bike rear cassettes. If you have any input about the other upgrades, I'd appreciate that, too.

Brakes:
The stock Tektro brakes are okay, just not the most responsive. Maneuvering tight corners in the city as a commuter and riding down long descents with a heavy load as a touring bike, it seems like the bike should stop quicker than it does right now. So I want to get a pair of Paul touring brakes with Kool-stop brake pads. I think this upgrade would improve the braking abilities significantly, but it would cost about $200.

I want to get a smaller chain ring, so a 26t to improve hill climbing abilities. This looks like the cheapest upgrade at about $15. Does a 26t v. a 29t chain ring make much of a difference?

I also want a new Mavic Aksium wheelset, because I screwed up the front wheel pretty bad in an accident. This has affected the braking, also. I can live with the wheels that I have. This really is last on my list of things to get for my bike, but I would if I had the extra funds.

Now what I need help on is this.
I want to replace the stock Shimano Tiagra HG-50 9-speed rear cassette(12-13-14-15-17-19-21-23-25t) with the Shimano Deore CS-HG53 9-speed rear cassette(11-13-15-17-20-23-26-30-34t) that's on the Surly Long Haul Trucker. It's mountain bike cassette, right? Lower low's and higher high's, but with loss of precision in the fine tuning abilities?

At least, that's what I understood from Doug64's comment in another thread
"Albert, I suspect that the 16t is a typo and it should be 26t? Depending on location , fitness, and load your present bike gearing may be fine for touring. However, you could get a pretty good all around combination by changing your rear cassette to an 11-34. This would require a mtn derrailleur such as the Deore or LX, and probably a new chain (longer). This will give you a lower low and a slightly higher high gear. The trade off is the wider jumps between gears."

The rear cassette on the LHT is only about $25, but the rear derailleur is a long cage. I was looking for long cage derailleurs on the cheap when I ran into the the Shimano Tiagra RD-4500, which is the same one that comes stock on a Cross-Check, right? Well, this website says, "The Shimano Tiagra RD4500-GS/SS 9-speed Rear Derailleur is a strong smooth shifting long or mid cage derailleur." link Is the Tiagra RD4500 that comes stock on the CC compatible with the rear cassette on the LHT

Thanks for all your help, guys. I've learned a lot here on BF.