100g in the rim is a fairly big difference tbh,if you think about it another way, would you want to swap your Crests for a 480g rim, like say a KOM i29?
But it does get fairly hard to beat out the last few grams, especially when the alu kit is already light and making sacrifices of strength like a Crest- there’s simply minimum volumes of material and minimum strengths that you run into. For me it’s heavier use where carbon worked out better, though not everyone will agree- I have the 390g 29er LB rims on my Remedy, there’s no 395g alu rim that I’d put on that bike. If I went alu it’d probably be an EX471, at 530g apiece.
Now some people would say, 140g a wheel isn’t a difference worth worrying about. And those folks obviously won’t be interested. I have a heavy duty wheelset with 560g alu rims (not so much because they’re that much stronger than my carbons, mostly because they’re cheaper- downhilling, rims no matter how strong are in the firing line and I’d much sooner damage a £45 rim!) and it makes a big difference to me.
Wheels strength is always hard to judge- strength and toughness are fairly separate, the wheel needs to survive whatever everyday hits it’ll take but toughness really comes into it with exceptions- casing on a rock edge, flatting a tyre and riding it out on the flat. Some tyres are strong but not tough (Flow Ex was a good example) And the rider makes a big difference to how many times you need tough- how much tyre they use, how tidy they are, how they ride and where, pressures etc.
For me, it comes down to what it took for me to break my original LB rim, a 360g 26er. I wrecked 2 middleweight alu rims on that bike, then replaced with the LB and it outlived those 2 alu rims combined by about 2 years. I eventually cracked it with a big stupid mistake which realistically could have damaged any wheel. My 29er ones have given good enough service that if I was to break one tomorrow I’d say, fair enough- especially if it was some riding error like that one was. (I just saw the price they are now and tbh, I’m not totally sure I’d buy them again! But only because of the 50% price increase)