How much is too much

[Synchro909]

Originally Posted by Dick Steinkamp

In order for the valve clearance to INCREASE with wear, it would have to be that the HEAL of the cam (not the nose) wore faster than the valve receded into the seat.

Having the NOSE of the cam wear would reduce valve lift but would not affect valve stem to lifter clearance.

I think it is unlikely that the heal of the cam wears to the point of affecting clearance in these low valve spring pressure engines.

X2.
Valve clearances are measured when the cam follower is on the heel of the cam. That is, when the valve is closed. The cam follower is only on the lobe when the valve is open.
To the OP, too much clearance will only cause noise and reduce the amount the valve opens. It will have a MINOR effect on the engine's breathing but not so much you need to worry. IF your clearances were set correctly when the motor was assembled, I'd guess it has done lots of miles by now for them to be that big. I think I'd let it run till it needs a rebuild and be confident your clerances are not going to cause a burnt valve.