I would scrape off the silicone with a wallpaper
scraper, then dig in a little if necessary. The
EZSand is OK, but it won't stop a crack unless
you use mesh tape with it.
I use Phenoseal for nearly everything. Siliconized
latex caulk is OK, but I don't find it to be as strong.
I don't use silicone for much of anything. It's hard
to clean up, tends to turn brown with age, resists
paint and attracts mildew more than other caulks.
I think the idea of using silicone for sealing bathtubs,
windows, etc dates back to a time when there wasn't
a good alternative.
I'll sometimes use Phenoseal for small wall cracks
on a budget job, but it needs to be sponged down
to avoid showing through as a bead, and it can't
be depended on to last. Mesh tape and compound
is the only thing I know that *really* fixes wall cracks.