Hey, lucky you! I hope I'm not too late to interject with some stuff.
First, I have the same bike as my tourer; it's my very favourite of the umpteen bikes I have. I think it's a fantastic bike. Here's my opinion on your questions (keeping in mind you used the words "necessary/cost effective")
- disc brakes?
No..... well yes...... but no if you're talking cost effective. Disc brakes are great -but IMHO are not great value. People have, and will, tour with non-disc brakes with more than adequate braking performance. Now for full disclosure I will add that my Sardar does have Avid road BB7 disc brakes, and yes, I love them. However, in retrospect for the costs involved (remember: new wheelset or relacing the rims to disc specific hubs, plus cost of brakes, plus cost of disc specific rack) make it a poor value proposition. Sure, since I've bought them and paid for them I'll keep them, but there's no doubt I would not buy them again if I was on a budget.
- new saddle - definitely required because at the moment it's like sitting on a rock - any good value-for-money suggestions out there?
So subjective any opinion is likely to just pure luck if it works. However, I can say I am one of the few who find Brooks uncomfortable (have been meaning to sell mine for quite a time now). The problem with a Brooks is that they are so expensive, so for value, again I wonder..... However, a saddle that is extremely comfortable can be priceless. You takes your money, you takes your choice.
- slightly larger wheels - there's a fair gap between the current wheels and frame, enough to go a size up for sure.
Strongly advise you to pass on this one. The Sardar is designed for 26 wheels. If you have a 700c wheelset try them and see if you can get them to work -but without discs I'd guess the braking alignment will be too far off for any v-brakes or canti brakes to work.
- pedals - just got standard ones at the moment but considering all other types, clipless, ones with toe straps etc
The general line of thought is that clipless are best -and I love my clipless. A good high value entry are Shimano 520s (I think that's the model). Be carefull though, some people just don't get on with clipless. I'd still give them a go. Keep in mind you will need new cycling shoes if you do take the plunge assuming you haven't got any already.
- tyre type - the current tyres are pretty worn so will need replacing by next summer - not sure about smooth road tyres of more of a hybrid tyre in case i take it off-road a bit. Having said that, no suspension makes any off-roading a bit of a sore one so I'm inclined to think it's not strictly necessary.
I love the Schwalbe Marathons. Great for touring -reasonably fast and tough. Might not be great for any off roading except gentle though. I think you also have to remember that when you want to do something on a bike that is not its primary purpose, you will always run into (sometimes less than ideal) compromises.
Oh, one last comment on brakes. It's been my experience that with brakes the fault does not usually lie with the brake itself -rather a combination of pads, lever pull, cables, rim condition and rim cleanliness. Before you jump for some new brakes, do the following:
i. clean you rims -thoroughly (Brillo pad and soapy water).
ii. check your cable runs and make sure you don't need new cables or the housing isn't gunking up the cables.
iii. make sure you brakes are adjusted correctly. Are your rims true?
iv. buy some quality pads. Can't recommend Koolstop Salmons highly enough.
v. if you feel you can pull too much of the lever, invest in some quality levers (a bit more expensive option here).
Note that most of the above takes relatively little money. Honestly, try the above first -even if you still think it's your brakes, you might be left with new cables and excellent pads to use anyway.
And don't forget that if you can't do anything much, just get out, smile and enjoy riding the thing as is!
