Q:

What PM certifications are worthwhile acquiring? 

I currently have two under my belt, I am Scrum Master certified, and Prince 2.  I have found that obtaining Prince 2 has been pointless, I never use it whereas the Scrum master certification was well worth the money, since I am using it everyday. 
I am looking towards obtaining more certifications, for heavily certified PMs on here, which ones do you recommend for digital projects?  I am having a look at PMP right now but not sure if it is worth the money.  Also, has being heavily certified impacted your employment prospects positively. 

A:

I don't know the answer to your question but I can advise you how to find the answer.   Look at the advertisements for the jobs to which you are applying and see what certificates they "prefer" or "require."   As well, if you get rejected, ask why and if they report a missing certificate as the or one of the causes, there's your answer.   
Thoughts on PMP: This certificate is used as a hiring filter in the space in which I work.   Though public sector--in which they are not supposed to use a commercial certificate as a filter--it is often a requirement or preferred.   As such, I value it in order to sell.   
As a certificate with hiring validity, I do not value it.   Anecdotally, I see no difference in performance between those who have it and those who do not.   Additionally, there have been studies, both on the PMP itself (Booz) and certificates as a predictor (Hunter & Hunter), that have shown very poor predictive validity, which matches my observations.   
That said, if you don't have to pay for it.  why not get it?   If you do have to pay for it, then see who is asking for it so you can try to determine if you're going to have a decent return on your outlay to get it. 