So on Blogger.com. I have a subdomain, bluh bluh. I built links for that subdomain already. So if I buy a domain name, a .com, how will that effect my serps and the back links I built already. I have over 200 back links built so far.
I doubt it will helps your serps at all. Not unless you can get blogger.com to permanently redirect your subdomain to your domain.
The best idea will be redirect your blogspot address to your .com domain.. you can use redirection url.. also start building backlinks for your new domain..