Another way of looking at it is how important to you is sitting in J?

If most of your travel is medium/long haul (where J is perhaps more important), you will eventually run out of eUpgrades if you are buying lowest T+ fare (and don't buy a lot of passes) and end up sitting in Y.

By buying the more expensive M fares, as an SE you will likely be able to sit in J (as long as space is available) on most/all of your medium/long hauls.

(This may vary somewhat depending on your travel patterns)