For me E-Vouchers are a total mess. I had 4 vouchers still in my account. As my +0,5 and Mother of +1 wanted to travel I tried to cash in the Vouchers for an Upgrade from Y to C (in a mid-booking class). The tickets were booked quite a long time ago. They took the LH combo because +0,5 needed Points for her requalification as FTL and the chance of an upgrade with my vochers.
When logging in the cash upgrades the pay-upgrades wer not possible any more.
Then on a regular basis I asked the HON-PAs what the chances are to get an upgrade (as the vouchers will only be valid till the end of the year and I have no other use for them). The answer: "The chances are very very good, but we cannot confirm it".
"Should I pay for a seat selection in Y?" - "No the chances are very high"
In former times a HON could ask the revenue department for an Upgrade- but that seems to be not possible any more.

A week before the flight +0,5 received an Email, that she could bid for the upgrade.
Then again I asked the HON-PA: "There might be still a chance".
Then my Evouchers were deducted from my account.
Next day, I asked for the real number: "Chances are very small", then I asked a bit deeper: "Waiting list is very long" - so basically no chances.

In the End it would have been better to buy a cash upgrade to Y+ to get at least a bit of extra comfort.
I asked the HON-Service for options, maybe upgrade to Y+ - but no solution was found.
The Vouchers are back in my account now. What makes me upset is the "we don't care" attitude of the staff. A few also said: "Oh that affects staff travel as well as it uses the same booking classes." I really do not care about staff travel as paying guest.

On the return flight we upgraded to Y+. I then tried to upgrade these with my last E.Vouchers. It took me 3 Agents to find out, that an upgrade with vouchers is not possible when there has been a cash upgrade.

Since I had quite the same issue with the vouchers I really do not care for them any more. I have a low chance to redeem them. When I want to use them it does not work as LH seems to wait until the last minute if anybody pays a few bucks. So there are not a reward for loyal guests, but just a disappointment. I would not miss it if the vouchers would be enhanced away.

Then with only 3 seats in F... No way.

As Always: Expect to sit in the travel class that you want to fly. Chances for an E-Voucher-Upgrade are low as you are at the end of the food-chain. They only upgrade you if they cannot fill the seats elsewhere.

PS: I do not need any PMs for others to upgrade. Won't do that.