Yes it is worth it and then some. An SSD upgrade is the biggest general performance increase you will get on a modern PC. Let me put it this way our 8 core Mac Pros with 32 gigs of ram at work running normal HDD's feel slower in general use compared to my little 2011 MBA with 4 gigs of ram with its SSD.
Go the MBA unless you NEED large internal storage, if so get the MBP and chuck an SSD in the optibay.
