I see that Jenson USA has a 72 hour sale going on and I've been window shopping. I'm going to pull the trigger and upgrade my tiagra front DR for an ultegra for $39, but I'm a little thrown off on which crank to look into. I'm running an Andel (I bought the complete CC) and am looking at either going ultegra or XT. I commute, train on roads, and where I live, rarely get the opportunity to actually race in any cross events. So do I go with the ultegra and swap out the rear DR and cassette for the trifecta, or do I go with the XT crank and upgrade the Deore DR to XT as well?
To be frank, while I'm buying the parts now - I'm not entirely certain I will race to swap them on. But a good deal on these parts is a good deal - and it will give me more incentive to ride the parts that are on the bike to death first.
IMHO, you'd save more money by leaving it in the bank (even at 0.25% interest) until the old parts wear out than you would by buying parts because they're on sale. If you're going to buy something, buy a rear derailer because they can get messed up if the bike (or you) falls on it.
This would be better off in the Mechanics forum, I think.
You want to stick with Shimano road hardware at 10-speed and below. This is what's compatible with your shifters. Tiagra is the highest still available, and par with what you have. The "trekking" rear derailleurs like the one you have are compatible but rare in the USA.
If you want to do a wholesale upgrade to 105 or Ultegra, look at Ribble Cycles in the UK. But I agree with @pdlamb, you don't save money by spending it
You won't notice any performance difference with the new front derailleur, so save your money. Same with your crank. Upgrade if you want to, but nothing magical will happen. Nicer/lighter tires and/or wheels would make a substantial difference.