No, blandish doesn’t only mean “sort of bland”. It’s also a verb that means “to coax or influence by gentle flattery”.
But it is related to bland, because both words come from Latin blandus, meaning “mild” or “smooth”. So, even though bland usually refers to something dull or flavorless, it can also mean “tranquil”, “soothing”, “gentle”, or “agreeable”. I assume that those more positive meanings are from a long time ago, because I’ve never heard anyone use bland in a good way. Have you?
Meanwhile, the word blandish doesn’t seem to exist at all! I couldn’t find any real-world example sentences – only Dictionary.com’s example: “They blandished the guard into letting them through the gate.”
I guess there’s no real need for the word blandish, since its synonyms coax and cajole do the job just fine. But hey, for all you poets out there, it’s one more rhyme for brandish.