SQL & PL/SQL :: Regexp_replace Function

I've been tasked to parse tags from a string that look like the following:

{Date + XXX}

where XXX represents a numeric value. I have to replace this, including the brace characters with

SYSDATE + XXX

which will ultimately calculate SYSDATE plus the number of days suggested by XXX. The problem is that I am trying to use regexp_replace to achieve this goal but since XXX is completely arbitrary, I cannot search for it as a fixed value. So, ultimately, I would like to use a regular expression that ignores the numeric part of my search and only replaces the starting brace, the "Date + " part and the ending brace, leaving the numeric portion intact. I was trying to do something like the following

myString := regexp_replace(myString, '{(Date + [^[::digit:]]{1,})}', to_char(SYSDATE, 'FMMONTH DD, YYYY'));

in hopes of making it ignore the numeric part but it, instead, treats occurrences as a non match. Alternatively, the call below

myString := regexp_replace(myString, '{(Date + [[:digit:]{1,})}', to_char(SYSDATE, 'FMMONTH DD, YYYY'));

matches correctly but replaces the numeric portion as well, so I'm left with just today's date instead of the calculated future date...