Other benefits should also be included in your consideration. For example Business check-in, FastTrack security, priority boarding, seat selection, onboard meal, and generally a better service. When you take all these things together with lounge access, then it may well be worth using some Avios.

That said, now that 'new' CE has less leg room, you may not find the actual flight much more comfortable than flying Euro Traveller (I'm not sure if you'll have 'new' CE to your destination).

As others have said, it depends how many Avios you have and how you value them.