Is worth change databases collation from Latin1_General to Modern spanish, migrating to a new server
Modern_Spanish and Latin1_General both support the same character set. The difference between the two is the treatment of certain characters when sorting/doing comparisons. For example in Modern_Spanish n and ñ are considered different characters (rather than a character and an accented version of the same character).

Personally I'd stick with Latin1_General as changing the collation may subtly change the behavior of applications (e.g. yesterday this list was sorted one way, today it's sorted a different way, etc.). I'd only change the collation as part of the migration if you understand and want the behavior change.