2002 V70 Estate intermittent engine stalling, partic in cold and damp weather

My usually reliable and good running 2002 V70 estate automatic has suddenly started cutting out/stalling, usually while bumper to bumper in busy traffic and (so far) only during the cold, damp early mornings. The battery is new.

At this point I should flag up that my ECU dashboard display has never worked properly so no error code is visible (it whirrs and flashes, occasionally showing that a bulb is out or a service is required, but otherwise it's just blank). But as the car recently passed its MOT (even with that blank ECU display evident) and has been regularly serviced throughout its lifetime, usually with no problems at all, that's never felt of particular concern. The car was given to me as a gift from a family friend, so it has cost me nothing except tax, gas and the occasional battery, bulb and tyres. However, that also does mean there's no dealer or past owner to blame or complain to!).

[Not sure if this is relevant or not, but another quirk of the dashboard displays is that in very cold weather, as soon as the engine is switched on, the temp gauge turns all the way up to max, and stays there. Took it to a motor electrical engineer specialist, who confirmed the engine temperature was fine, that it was probably just old, slightly cracked wires with damp getting in (he stripped and re-cased with thick electrical tape all that appeared worn].

Obviously, I'm thinking that the ECU may be kaput, or perhaps on its way out? I've heard it's possible to replace it, but it's expensive (approx £1500 + labour). So my first question is whether that kind of cost sounds about right, if that is found to be the cause?

And secondly, in your opinion, given the car's reliability and comfort thus far, would you invest the same £1500 in finding another old V70, or has it been well worth the repair investment, in your experience? The chassis, exterior and interior are still in great condition. I love this car and the fact it was passed on to me by a great friend means it has sentimental value too (I know, we all get emotionally attached to a beautiful old car!).

I know nothing about cars so I bow, with great respect, to your wisdom and generous sharing of Volvo expertise!