I have a Specialized Ruby with compact 50-34 chainrings. It had a 12-27 rear cassette. This was not working for me in the Santa Cruz Mountains. There are places with over 10% grades. I changed the rear cassette to a 12-32 IRD (since Shimano does not make a wide range 10 speed cassette). I changed the 105 short cage derailleur to a 105 long cage derailleur and a new chain. Now the bike can do hills much better. Even with this setup, I see even more experienced riders with even lower gears than I now have. I can see how much more they spin than I do. Many of them have triples (or mountain bike triples) with 11-34 cassettes. So, if you are going to make some changes, I would recommend going even further than you are planning since the expense would probably by similar anyway. Of course, it depends how steep your hills are.