I would put the odds on what you want to do working as planned at no greater than 20 percent. Record consolidation would be very smart as I am concerned that YOU won't make it, forget about the bags. PHL LGA is notorious for delays. Adding bag retrieval and reclearing security almost guarantees a fun filled evening at the airport.
Without consolidating the records, if you miss the flight out of LGA, I think you will be asked to pay ticket change and the same day ticket fare, which I am confident would be a punishing number. The cost of record consolidation might be cheap insurance against missing the plane. More experienced FT'ers can probably answer that.
Either way, I would have a change of clothes and anything you need to overnight with me in the event you get stuck. The nicest reasonably priced hotel near the airport is the Hampton Inn. It is fairly new, clean, and the staff is friendly. They have a free 24 hour shuttle.

PT