Excuse my long winded reply, but there are a lot of issues here.

1. Regarding vouchers (for DECB) making it essentially "free" to get these, let's consider some actual math here.

I have 1k plots (not even top 25), that's 10M DECB needed to get the survey boosts. 10M DECB / 200 per voucher is 50k vouchers needed. I (used to) have 2M+ SPS staked for a long period of time,(top 25) yet I have nowhere near 50k vouchers.
That's at least partially due to the fact that I've been using those vouchers for their original intended purpose of giving access to "all the cool stuff." But it's certainly NOT essentially free to anyone who hasn't been hodling every voucher they get from staking.

2. These have been talked about a LOT as being an optional thing. Making them double your chances for every better rarity and resource is NOT optional for anyone in their right mind.

3. "We see only upside for SPS token holders from this proposal"

Really? Because I've been unstaking and selling my SPS like a mad man to try and have enough DEC to cover this unexpected expense. Not sure how that translates to something good for SPS holders. Certainly not good for my SPS holding.

4. The people who bought land in the original sale paid anywhere from 7.5k to 20k DEC for their land plots. Those of us who have held our land even through the $1000 peak are arguably your most dedicated supporters. Tacking on an additional 10k DEC(/B) to our purchase cost is extremely disheartening and hurtful to your biggest supporters.

There are other things I could talk about as well, but they've been hashed out in the discord quite a bit, so I'll refrain from writing it all here.

In summary, this is not a good idea. Build an enjoyable engaging land gameplay and you'll get your "DEC to par" dream to come true. Trying this thinly veiled tax on the most exciting thing in the Splinterlands ecosystem is not going to help anything here.