At least with the bonus block you can pull off the duplication glitch to theoretically receive infinite 1-ups upon collecting 30 coins. Then again though, you could do the same thing to a regular 1-up block and a Yoshi block, which involve far easier methods than using the bonus block. With that said, you would have to take into account what levels even have these blocks at all.
Yoshi's Island 3 has both a Yoshi block and bonus block, so the former would likely be the more favorable pick in this case. Butter Bridge 1 has a 1-up block and bonus block, but since the level is an auto-scroller, you'd barely have any time to pull off the duplication glitch with the 1-up block. The bonus block is at the end of the auto-scroller, so going through the task of collecting 30 coins would be more worth it. Donut Plains 3 also has a bonus block, though considering its position, which is over a line-guided platform that falls off by the goal, you'd be better off trying for the 3-up that comes from scoring a 50 on the goal tape than perform the glitch.
The bonus block itself is an interesting entity. It doesn't seem to have a reason to exist at first, when compared the previously mentioned blocks, which fill the criteria of bestowing a 1-up upon the player. Though with those blocks, it's far too easy. Giving the player an extra life is more of a reward for certain actions they've done, like collecting 100 coins or 5 dragon coins. The bonus block serves this mindset, by presenting an extra challenge for the player to face with a payoff at the end. I personally don't see any harm in this block being used more in ROM hacks, considering its appearance was lacking even in the original game.
--------------------What is a Lunar Magic, and can I eat it?