Upgrading road bike

Have to agree with above, tyres and wheels first. Replace the drivechain when it wears out with the best you can get, emphasis on the shifters and then the chainset. There's no real need to go above 105 but Ultegra is nicer.

Think this thread has just convinced me to buy some new wheels. Damn you Sunday morning insights!

In order of priority:

Tyres
Wheels
Groupset
Whatever's left

How you do it depends on the aim and whether it's comfort or speed thats most important.

Tyres can improve both and also how the bike handles. Get good puncture protection. I ride schwalbe Durano or Ultremo.
Better wheels can make you faster and climb better. PRO-Lite Bracciano here.
A better gruppo will shift better, weigh less and look more bling. Aim for 105, but remember that the shifters are the key element. I ride Campagnolo, but know how well regarded 105 is.

I was in your situation and bought a new tighter ratio cassette, some 25mm 4000s tyres (check they will fit) and some second hand as new aksiums. Transformed the bike. Cassette makes for smoother feel changing up gears, wheels were 500g less weight and tyres were quicker, more grippy and cushioned the ride more. I got most of it as new from eBay.

I'd look at;
Gropset to 105 (Can pick this up for around £380 now and is easily worth the £100 over Tiagra)
Wheels. I rate my Racing 3's, 3 years and never caused me a problem, But they're £400, Quattros get decent reviews and are less at £240.
Tyres, Something decent like a Conti GP4000S, or Vittoria Open Corsa Evo CX. These will make a surprising difference in terms of cost compared to the rest.

Anything else you think isn't 'right', saddle not feel good, bars too deep/shallow, stem too long/short.
Things that make you more comfortable and in the best/efficient position will do wonders than a groupset weighing 250g less.

I would go for Ultegra. It's the top step before you really extend yourself. Dura Ace is massive step up in price. But from 105, the step to Ultegra is affordable. In my opinion the shifting is a bit cleaner and crisper.

Getting ksyeriums was one of the best things I did. And if I had the money I'd get the SLs in the range.

Why not pimp out your bottle cages in carbon if you have the money.

If you're going to upgrade the groupset, no need to go higher than 105. I have a 105 bike and an Ultegra bike and I can't tell a single noticeable difference at all other than looks. No need to spend a huge amount of money on wheels either. My Fulcrum Racing 7s don't make me any slower than my Ksyriums.

be smart with upgrading the drivetrain, a rear mech is pretty much a rear mech, but good shifters do feel nicer than cheaper ones. A chain set is a chain set, although there is a decent weight saving going from cheap to very expensive.

Place to start though is tyres, i like Michelin, others swear by Contis. Just get a reasonable set Pro4, gp4000's, etc.

Next wheels, the more you spend the better, within reason. But have a think if you want light or if aero is more what you want. And be realistic, carbon rims might be in vogue, but are they really practical for commuting to work, winter riding etc.

Nothing wrong with the allez frame and anything other than a 2300 groupset will feel like dream. Personally I would look at a minimum of a tiagra groupset as a minimum, ideally ultegra if the ££££'s can cover it or 105 if not. For wheels, fulcrum 3's if possible but fulcrum 5's are ok. Don't know what your budget is but a cheap improvement can be gained from shifting to continental GP 4000's (just over 50 quid for a pair on wiggle at the moment). However, winter might not be the season to do this !