Boosting profiles - paying connects for profile clicks. Best strategies?

So I've pretty much avoided ever boosting proposals or paying for the availability badge, however I have seen a few people suggest that paying for profile clicks has been an effective strategy for them, especially now that it seems invites are much more valuable vs applying to jobs that have 50-100 other applicants. I'd be curious to hear from anyone who has done this successfully.

• How much do you bid per click / limit the total connects to?
• Did you schedule an end date and test different categories or specializations?

I asked that 2nd question because I do both branding and web design / web development, and get hired pretty evenly between the two. I see that it makes you choose one main category and one specialization, so I'm torn whether I would choose for example CMS Development vs Font-end Development vs UX/UX design. Curious what others have done who may be in a similar situation.