Route53 doesn't allow multiple definitions of the same name/type pair of DNS entries which is quite a headache. This is the first time I've had a conflict of a TXT record in Route53 at the base, specifically both Google's site verification, and SPF records both want to live at the root of the domain. The site verification record needs to stay around as Google periodically re-verifies the domain.
To get this to work you need to quote both the Google verification string and the SPF record, but you also have to ensure that there is a newline in the field. The contents of the entry should look something like this:
"google-site-verification=<auth string>" "v=spf1 include:_spf.google.com ~all"
You can use Google's MX Toolbox to verify the SPF record.