Still, you are correct that it just proves that I am ready for gold--fighting against Cerberus at least. (The Collectors are another question. I hate the Collectors.)
Moving from Silver to Gold, you may find your preferences change a little. On Silver, Collectors are undoubtedly the hardest enemy faction, while on Gold the difficulty jump by Cerberus is significant, making them the hardest, with wave 7 in particular often causing major headaches. If you ever make it to Plat, that's when the Geth truly come into their own.
The TSent is one of the most versatile characters in the game, and he can cope with anything, but don't underestimate the Asari Adept. Clyde might disagree with me, but her Stasis bubble combined with a headshot-capable weapon with headshot bonuses can absolutely trivialize Cerberus, and make you one of the most popular teammates to have, keeping Phantoms at bay.
As for the wider question of challenges, I'm with Al - they gave me focus and variety and made me a better player overall. I'm just messing about now with two low-level accounts, having made it to 130k on my main, and I notice myself dithering over what to play next a lot of the time - that wouldn't have happened when I was working through challenges. I'd like the concept expanded for Andromeda, so that challenge completion is in some way tied to weapon and gear unlocks. I suppose I can dream!