I think it's worth waiting a little more to see how this turns out, since there's a lot Riot mentioned about plants that didn't get conveyed in the videos, plus this is still very experimental stuff.
With that said, I share the sentiment. As a jungler main, I agree that Smite buffs ended up not being interesting at all, but I don't think these plants are a good replacement, or really a good way of adding "diversity" to the game. Yes, League does feel like a solved game after a while, but there are a ton of reasons for why that is, and none of them will be answered with random power-ups. For one, there's the issue of the game still largely revolving around marksmen, which has been around for most of the game's lifetime now and still hasn't been addressed, despite massively locking up diversity in team comps, strategy and overall gameplay. There's also the issue of games feeling like they're decided way too early in some cases, a factor made worse by Preseason 6's minion snowball system. On top of this, diversity always contracts periodically whenever some flavor-of-the-month build/champion makes others unviable, which is currently the case with Rylai's/Frozen Mallet sidelining a lot of melee champions.
What annoyed me the most when watching those videos is that they all made it look like whoever used those plants were arbitrarily handed out a get-out-of-jail-free card. Perhaps there was much more tactical gameplay, in that the players knew where those plants were ahead of time, and moved towards them to get that bonus, but we didn't see any of that there. What was also annoying is that Fearless mentioned how plants were supposed to un-solve "fights that have trended towards predictability and being solved" (his words, not mine), yet when I saw all of those situations in those videos I wanted those fights to be solved. Graves committed and went into the enemy jungle, Karthus blew his ult on a correct target, and Nunu put himself at risk to get a sneaky solo Drake steal. By contrast, all Jayce, Gnar and Lee Sin did was basically hit a plant and win, each one countering a play that took a lot more effort or resources to pull off. Sure, those plants added variance, but it felt like the wrong kind of variance, and variance in the wrong places. Adding random or pseudo-random power-ups might add some novelty to the game, but it's not going to add that much more freshness to each new match unless Riot really makes them game-changingly powerful, which I absolutely do not want.