You figured out Plots and Totems aren't efficient. Buying SPT isn't either although getting some free ones from posting is a great way to get SPS from airdrop then stake for Voucher.
Now assume you wanted 300 Power...
Buying the DEC costs you $3.60
Buying cheap cards (60 heatsmith at .15 @ 5 Power each) costs you $9
Or you could just buy a Chaos pack at presale price which costs you $8.58
I also want a few CHAOS packs to get in on the initial opening but rather than buy them through Splinterlands where I get the possibility of airdrops and 50 card promo's I'm just buying the regular packs.
A voucher plus $4 is $18.79 or a pack costs $8.58. Sure its double the $4 price but for that price I get a pack later and SPS airdrops in the meantime. A double win :)