People work hard RuneScape gold for high Agility levels, this would be a nice way for them to see a little return on that work without it being an overwhelming advantage. I am also adding into this suggestion the rate in which you fail obstacles.
It's kind of ridiculous that at 70 Agility you still fail the log balance in Ardougne, or the jump from Barbarian Outpost to the Lighthouse. Why don't obstacles scale in pass-ability that a word similar to how the odds of burning food does with cooking.
The amount of exp gained from the penguins could even be reduced slightly so that it doesn't feel like something that MUST be done and only something extra that would be a nice break alternative from the typical way to gain exp once per week.
Penguin Hide and Seek was a very fun diversion that also got buy RS gold you some pretty respectable exp. When I say to add this, I don't mean all the quests that gave additional points, just the basic 10 penguins to hunt down. To appease the purists.