I think you are right. The date is coincidental. The significance appears to be from bombing the crowd/participants at a high-profile sporting event, (terrorist act), rather than a specific political statement.
If "Tax day" or "Israel's Independence Day" were the significant motivators, the terrorists would likely have chosen target(s) more closely related to those topics--an IRS office or Israeli consulate--rather than the finish line of a footrace.
The act was aimed at rattling the masses, or the devices would likely have been placed where dignitaries would have been more likely to have been injured.
People using explosive devices to protest something tend to remain focused on what they are protesting, and that affects their selection of target(s). These appear to have been shrapnel laden (antipersonnel) devices, aimed at people, not structures.
Because one could reasonably expect the crowd to contain people of all backgrounds and political views, the objective appears to be one of terror, not a specific viewpoint or policy.
I’m in total agreement with your assessment.
You just said it way better than I did.
Considering what I’ve heard some people saying (I forget who they were interviewing on Fox), but these types of bombs that were used, are the same kind used in places like Iraq/Afghanistan, where they blow them up in strategic places, to get people to run in a certain direction, and then when the crowd goes in that direction, that is where the main bomb is set to go off, to get the most impact.
Luckily, the cell towers were shut off before that kind of thing could happen yesterday. But they did find, from what I’ve read, 5 more bombs, bringing the total bombs (found anyway) to 7. I can only imagine what these terrorists had planned.