First thing to say is that if you're looking to buy an Ion, just buy it. Don't worry about what year it is, they are all fabulous.
Nicolai seems to have a process of continual refinement in its designs; these are never radical changes, nothing that is ever billed as being a 'relaunch' or 'version 2.0' or anything like that. Just small evolutions of the same proven design. For example the switch to 1.5" HTs on the AMs (from 1 1/8th) or the inclusion of ISCG tabs as standard.
With the Ion ST, the biggest change came around 2009/10 when I believe they slackened the head angle from,65.7 degrees to 64.5 degrees and the BB dropped by 15mm from 25mm to 10mm (which is a huge change really!) They did a similar thing with the AM and the AC as well - both of which lost 1 degree in the HA.
Also the head tube is now 1.5" but that is a more recent change I think.
The changes to the rocker links you've highlighted are probably nothing material to frame in terms. From 2008 to 2009 there were also very small changes to the fabrication; the earlier versions had a solid member between the lower part of the forward link and the down tube. By 2009 that strut had been machined out.
Personally the change in HA would be neither here nor there; mostly it makes a difference only in the brochure. I never found the 65.7degree HA steep, but then I don't have the kind of ground speed where it's going to be noticeable. The lower BB most likely will feel very noticeable, but again the BB on the older model never felt high - at the time a sub 14" BB on a bike with up to 230mm of travel was considered to be very low. Now suddenly we're dragging our knuckles on the floor with borderline 13" BB heights!
If you want to reference anything, here is the 2008 catalogue link, which has the original geometry for the Ion when it was launched:
Hope all this helps and get that Ion bought - it's a wonderful bike, so neutral and well balanced. You will NOT be disappointed.
FWIW I have an 08 style ION and I would say the bb height is perfect. Any lower and it would be peddle strike city.
maybe a bit late but anyways...
first production series Ions did have occasional problems with the rocker links bending when ridden (very hard) in the hi-travel position. the bottom picture shows the beefed up version which was made available to all Ion owners with the old links. all it costed was an email^^
i have a 2010 Ion with the slacker geometry and the low BB in combination with 175mm crank arms, can be a PITA and is a real pedal bender... gotta get some 170mm