Yes, you probably should care. Even if you don't want to go any faster. Your neighbours want you to care too.
Why should you care? It might not be obvious now, but it probably will become obvious over time.
Back on ADSL, your biggest enemies were the distance from the exchange, and noise caused by line errors or interference.
Now you are on FTTC, and are getting 70Mbps, you've already shown that those 2 factors can be ignored. The replacement factor - that you're close to the cabinet - is less of a factor too. You're probably within 400 metres or so.
But your last remaining enemy, and now the biggest enemy, hasn't shown its face yet... it is the group of other subscribers that are being added to your cabinet over time.
As subscribers are added, the signals to and from their modems are picked up by your telephone line, and appear as noise to your modem. This is called crosstalk - and the more subscribers there are, the more crosstalk you will see. Some subscribers will have little effect on you, while some will have a dramatic effect. Your line is having the reverse effect too.
The added noise from crosstalk means that either you will lose some of your speed, or you will suffer from errors and packet loss. DLM will turn on interleaving & FEC to correct those errors, so you will see increased latency and a reduction in speed.
The effects are random, but mean that any line could lose 40-50% of its theoretical top speed. That might not mean much to people 100 metres from the line (where most people will still get near 80Mbps), but at 1km range, the drop can take people down to 25Mbps.
Vectoring is a smart process to remove the crosstalk, so your modem gets a cleaner signal. There will still be noise from other sources, but the signal should be better. A better signal means fewer errors
Where do things go from here?
Well, with a better signal, you can do two things: a) Run at a higher speed, or b) Run at a lower transmit power.
So, if BT chose to, they could probably add packages at 100Mbps, or possibly even 120Mbps, and let you run at higher speeds. Trials in other countries show that 100Mbps is a plausible speed for properties within 300 metres, and possible within 500 metres, depending on the state of the copper wires. BT haven't run public trials yet, so we don't know how things will fare here.
BT could also choose to not introduce higher top speeds, but to allow modems to run at lower power, at least for closer subscribers. At lower power, it is possible that these subscribers would have even less impact on the more remote customers, especially if vectoring is less than perfect at removing crosstalk. The more remote subscribers would get a better signal, and get a speed boost up to closer to theoretical limit for their line.
For customers between 800 metres and 1km from the cabinet, vectoring could improve their speed from 25Mbps up to 40-50Mbps.
That's important to BT because somewhere in the region of 80% and 90% of the country are within 1km of their cabinets (if they have cabinets).
Finally, the technical problem to all this... Vectoring only works if it can work on all the lines from the cabinet in one go. For BT to get any advantage from this at all, even for a single customer, every subscriber on the cabinet must be vectored.
So, to answer your questions:
- No, it won't make much of a difference to the best performance you are seeing now
- Yes, it could make a difference to you when you cabinet is running full, and your top speeds have fallen away
- It will certainly make a difference to your neighbours living 500 metres further away.
- BT aren't likely to reset the 18 month contract just to put you on vectoring.
- But if BT introduce higher speed packages (say 100Mbps) and you want to be on them, I suspect a move is likely to trigger a new contract.
But... it hasn't even gone to a live trial yet, and I guess that BT will want to try a lot of things out to balance between higher package speeds and lower power; between speed improvements for closer lines and improved range.
The only answer is to keep watching.