Should I change my gearing?

I picked up a vintage Specialized Epic road bike a couple of months ago and have been enjoying riding the bike. I'm concerned about not having any low climbing gears. The front rings are 52 and 42. The 8 speed rear cassette is a 11 to 25. I have avoided any serious climbing with the bike so far and have found I have been able to handle minor climbs fine. I'm concerned that if I took this bike where any serious climbing was involved, I might go anaerobic before hitting the crest.

I was considering putting a 11 to 28 cassette on the bike and changing the 42 tooth front sprocket to a 39. The rear derailleur is a short change Shimano 600. The front derailleur is Shimano 600 also.

I'm not sure the derailleur would handle the gear inches and if the changes would be worth the cost. It shifts flawlessly right now. I'd hate to mess up a good thing.

What do you guys think?