there are only use words can be used as adj.+一点，like 高兴一点，开心一点，振作一点，精神一点etc.when you try to encourage or comfort someone,we can use senteces like 你别这么伤心了啊，高兴一点. (don't be so sad, cheer up.) so it doesn't apply to words like 伤心(sad)，沮丧(upset)，etc. and as for" 有一点+adj" it can apply for all kinds of adjective,it means a little bit.

"adj.+一点" = a little bit more 高兴一点 = a little more cheerful; cheer up "有一点+adj." a little 有一点高兴 = a little cheerful Otherwise the rules by Jessetao apply.