Maybe I get you wrong, but @Model.StartPublish (or @Model.Changed) will give you the "last changed" date. No need to dive into versions.

However is you want to create a list of change dates you can use this code:

var cvr = ServiceLocator.Current.GetInstance<IContentVersionRepository>();
var publicationDates = cvr.List(currentPage.ContentLink, currentPage.Language.Name)
                                    .Where(s => s.Status == VersionStatus.PreviouslyPublished).Select(p => p.Saved);

Thanks!

I use this for finding out if the Changed date has been updated:

DataFactory.Instance.ListVersions(page.PageLink, page.LanguageBranch)
    .Where(version => version.Status == VersionStatus.PreviouslyPublished)
    .Any(version => version.Saved < Changed);

and then I print out the value of Changed if the code above returns true.