SLIGHT RESERVATIONS The most simple answer to this question is no, because 84 of the 100 most expensive Commander-legal cards are on the Reserved List
Passively playing creatures from the top is great as well, and it gives you more opportunities to set up the -2 for good value
Then you can -7 as an ultimate to have your foe exile X cards from their library where X is your exiled mana cost, so that's a win-con over time
Gems From the point of view of spending them, gems and gold work similarly: Pretty much everything you can buy with gems you can buy with gold, too
You also get a guaranteed foil card, and it can be of any rarity, including borderless rares, Transformers cards, retro artifacts, retro schematics, Jumpstart cards, or Commander cards
The same is true if it converts before combat damage, so be careful with that second spell