It may be "worth it" in relative terms but
IMHO that a little extra for the DG APO version is more VFM in sofar as the non APO version sells for £90 new
If you can, I would also ask you to consider a Zoom lens with IS.It makes a lot of difference especially if tripod use is not always expedient
Check Onestopdigital for the Sigma APO DG Macro (red ring) which has the additional lens coating. It's a very good budget zoom, but the gearing is cheap plastic.
Unless you fork out £295.00 for the Sigma DG OS version, the other budget alternative would be the Tamron 70-300mm Di LD.