you get a fair bit but more on a weekday, you usually see class 66`s and 92`s more than anything else, I agree with what geezertronic said, best places in the Midlands are
Tamworth
Water Orton
Nuneaton
Stafford
Crewe is also good but a few things use the avoding lines, I recomend a
West Midlands Day Ranger, You can use it anytime on a sat and if you have no luck at international you can try somewhere else, prices are on the website but the railcard price isnt showen so ive put it below
Adult
£16.20
Railcard
£10.70
Child
£8.10
need anymore help just ask, im often out and about around those areas so I can tell you everything I know.
also is it the 28th your going? there is a 2x Class 37 railtour starting and ending at that station but is there early and finishes late
Railtour link