I currently have a 2010 Dawes Horizon (see here for specs: http://www.dawescycles.com/p-25-horizon.aspx). I am planning a trip through South America in early 2013 and believe some changes to the bike will be necessary to deal with the steep Andean climbs and the scarcity of bike shops. I used the bike to travel from London to Istanbul and had barely any problems - except for an issue with one of the brake cables in Croatia.
I have considered selling the bike for whatever I can get an investing in a Surly LHT, clearly a superior bike. However, if the following changes can successfully be made, it may be more economical to work with what I already have.
Some changes I would like to make include the following:
1. Although 26" wheels are probably more suited to regions such as South America, the 700c wheels will have to do (I can always have replacements ready to FedEx waiting with friends in Brazil should anything go wrong). However, to reduce the chances of this happening do you think stronger wheels are required?
2. Changing the STI shifters to bar end shifters would also be desirable as they are less complicated etc. and so more suited to South America.
3. Possibly the most important change, and one I desired when cycling the Alps, is lower gearing. I think an 11-34 (or, possibly a 11-36) Cassette + 48-32-22 or 48-34-24 Crankset would provide this.
4. It may also be worthwhile changing the Alivio gears to either Deore LX/XT
5. Finally, I screwed the fork a year ago so I will have to replace the existing one with a new one.
I would appreciate your views on the above suggestions (and if possible!), and if anyone could ESTIMATE a price for having this done that would be great!
I don't know prices for your market, if you've got a lot of miles and wear on those wheels I'd go ahead and replace the rear wheel for peace of mind with something as robust if not moreso, you don't state your load so it's hard to know if they're up for it but your trip to Istanbul sounds like a testimonial.
Regarding gearing I'd look to practical gears which are the lower ones you mention but the ubiquitous 11 tooth cassettes with 48tooth chainring gives fairly useless high gears. Replacing chain rings can get close to the price of a new crank. I'd be more inclined to get a 42-32-22 Alivio since the 22 inner ring will get you the lowest gears with any wheel that comes your way. A 42-32-22 Alivio with a 11-28 8spd cassette would give you a 10% lower gear than your existing set up with closer spacing and more usable high gears.
Regarding a new fork I'd look for something that could allow for a fatter tire without changing the geometry too much. Surly sells the LHT fork separately. Assuming you're in the UK it looks like Thorn forks are a good choice.
All of this might cost 1/2 of your bike new but as you've discovered with the fork stuff happens.