That could really be a good move - but there is some risk involved. Vouchers could definitely rise for Rift Watchers. But it is not clear yet, how many vouchers are needed to buy packs - and as far as I remember there was the plan, that you'll need SPS to buy RW packs.
Right now, for most people vouchers don't really have a lot of use - and it can take quite some time, until Riftwatchers will be released. Until then Vouchers are more or less dead money. You could put them into a liquidity pool with DEC to collect more SPS airdrop points, but that is almost it. If you use the same amount of money on SPS or DEC you can get higher airdrops or staking rewards.

Many asset prices are very low right now. It might also be an option to load up on cards. Or if you want to invest more, Land could also be an option.

Don't get me wrong. I am not saying that vouchers are a bad investment or it is a bad idea in general. But the usability is pretty limited right now and for the time coming, while other assets have (in my opinion) more value - and are also quite cheap.

No financial adivse though.

Cheers,
@andy-plays