What difference does an upgrade make?

In real terms, not very much to be fair.

Is the dale rim or disc?

Di2 is nice, but not a game changer for me, admittedly I'd still rather ride with it than without though.

The Synapse is a lovely bike, they are pretty light by all accounts, I had a 2016 Ultegra model with Di2, and still have a 2015 one I need to sell actually.

IF it fits you well, and you like the look of it, have you considered spending a proportion of that 3k on new wheels, and a di2 groupset?

The other difference with the new bike will be fully integrated cables (Though these look lovely they are more of a pain), and gear ratios, your Dale will be 11spd, the new one will be 12spd, so you'll have a slightly wider range of gears, but you could get around that with a new 12spd groupset and some new shiny wheels for the dale of course.

Mind you, if you have a hankering for a new bike, and it makes you feel good and want to ride more, then I'd go that route :-)

Would you sell the dale or keep it as a turbo/winter bike?

2nd hand market is pretty weak right now.

As Dan says, the difference between those two particular bikes will be fairly negligible. The feel and ride quality may vary a bit, but whether that is an upgrade or not is purely subjective. In terms of a performance upgrade, it will be minimal.

These days the real jump is someone going from a budget bike, say a grand or so up to a well specced £3.5-4k bike. That's where you will notice a real difference. Even from £4k to £10k now the difference is minimal, you are really paying to save weight.

That's interesting - the same place offered me £1100 for my 2016 disc brake Ultegra Di2 Synapse, with very low mileage and unused wheels/tyres and saddle. It retailed at £3200 new iirc. I sold it privately for £1950 - this would have been late summer 2021 I think. Perhaps times have changed, but at the time it certainly put me off them. I know people who have had success buying bikes from them however.

If your current Dale is rim brake, a big change would be disc brakes - I think the latest Ultegra 12spd callipers have that little bit of extra space, which makes the frustrating rotor rub slightly less likely.

The Dura Ace levers also extra bonus buttons on top of the hoods, though not sure if the Ultegra one has that too.

You can also choose what the levers do using an app that connects over bluetooth, and I think you can set up some kind of auto shifting thing as well, ie when you drop down from big cog to little cog it will go up two gears at the back, and vice versa - I should really have a look into that in more detail.

If you do your own mechanics currently, imo you'll find fully integrated cabling and hydraulics make that more difficult - if you have the time, and can learn the new skills, all well and good, otherwise it will be paid services at a suitable shop.

I used to do loads of mechanics, built bikes up from frame and parts, cut steerers, fitted bottom brackets, headsets, the whole 9 yards, but since becoming a parent, and slowly mostly moving to disc brake bikes, I find I don't have the time, and what time I do have I want to spend with the family/doing nice things, cycling etc etc

That's the other thing if you are not doing your own mechanics and went the new groupset route, you would need to factor in the cost of having someone remove the old groupset and fit the new one as well - probably somewhere around £100 - £200 depending on whether it is a shop or a home mechanic.

If you are looking for new rim brake wheels, as wheelspinner mentioned, there will likely be a ton of bargains out there that will suit for reasonable funds.

I stumbled on a stunning deal for some barely used Enve 6.7s a while back, and they were truly mint, and about 35% of retail - stripped off the original decals, had some customised colour ones made up which I then fitted, and you wouldn't know they aren't brand new.

@carbonrox for rim brake options, are you thinking carbon or alloy? You will likely get the most performance upgrade from a aerodynamic carbon rim and there are plenty of options out there (starting at around £600ish).

If you wanted to stick with alloy and have a brand new wheelset, I would buy a set of these.

I have a pair and they are very good wheels, under £300 for a £1400g wheelset is pretty much about the best VFM in an alloy clincher you can get IMO. Something equivalent from Mavic or Campagnolo now would be around £800.