The problem is that the set of GUID far outnumbers the set of all integers long precision. So really you are shrinking the cardinality of choices significantly. There is no good reason to do this.
If you want to keep increasing a number and not worry about it, there's a library IntX that handles big numbers. You could store the local state of your number generator in a file or in memory and you'll have an ever increasing number. (well sort of)
