You can stake SPS to get the vouchers, AND THEN unstake to purchase RW packs. RW won't be released for 4-5 months, which should be ample time to accumulate some vouchers before unstaking to purchase.
However, as I'm sure many others will tell you, if you want best value for competing, buy individual cards.
RE: Splinterlands Town Hall Summary - January 7th, 2022 - 2PM Eastern!