I'm happy to keep effect expiry (limited lifespan) items in the game, I personally don't think its as powerful as you're presuming.

The reason why effect expiry is not as powerful as you'd think is that as you increase the level of the effect (adding uses per day and penetration etc) your lab total exceeding the effect level drops, while at the same time the required points to instill the effect is reversely raised. Soon X2 multiplier isn't enough to be able to create the item in a single season.
Also remember that this effect does not allow a magus to create effect's he would not normally be able to, it just shortens the time it would normally take him to produce.

Yes the 70 year expenditure is unlikely to come into play; though at 2 game years a session, say 5-6 sessions a year that's only 6-7 years of play, so it's not out of the realms of possibility.
If people are really concerned about game balance I'm be happy to see something like the effect expiry cut in half to 35 years, at least that way it will impact the game in the future. But in general I don't think its that big a deal.