I’d say they are saving up something big for the 054B rather than incremental upgrades.
IMO it seems that 052D and 054A form one “generation” of ships. The 055 represent the DDGs of the next generation, so there should be a next generation FFG in the pipeline too.
The whole point of going all AESA in every radar, including navigation ones, like the Type 055, is to ensure every radar has LPI (Low Probability of Intercept) mode. Means the radar has the agility to make waveform using pseudo randoms jitters and staggers, to make the waveform look like background noise or static, which isn't going to trigger enemy's ESM. The ESM would regard the signals are mere noise, not radar. This gives the ship a "stealthy" radar profile.
A ship using its radars can be a beacon to the enemy telling that it is there. If a ship has one main radar that is AESA and has an LPI mode, it can be undetectable while this radar is on use. However, the ESM can pick up signals from the other radars that are not AESA. That's the issue with the Type 052D, which still has a bunch of mechanical radars, including its Type 517, 364, 366, 344, navigation radars. The 054A/P still has the 364, 344, 366 and navigation radars.
The guy who drew his CGI concept of the Type 054B might know a bit more. His design is an all AESA one, including search and navigation radars. Note the radars on top of the bridge. He really thought of everything but only forgot to put the ECM. With the exception of the very short range radar on the CIWS, every radar is an AESA and the ship can generate an all LPI profile. I would expect the Type 052E to take this route too --- convert the said remaining legacy mechanical radars of the 052D into an AESA equivalent or integrate its function to fewer multirole AESAs.
Of course, there is more to the 054B fan concept too. The PLAN now seems to prefer this CIWS layout with gun CIWS on front and HQ-10 in the rear as standard, and the CGI incorporates that. The ship may have moved to using U-VLS, which is logically speculative. There is the IEPS. The ship's general appearance may also be a bit more passive radar stealthier. Might have two helos to shelter.
But if you are really after a 'mere' performance upgrade that is massively cost effective, the 054A/P does this. 'Mere' is understating, the SR2410C is a massive leap over the Type 382 in terms of generations. No question the point of YJ-12 over YJ-83. If you don't want (or cannot afford) an all AESA-LPI ship, and simply go for performance, the 054A/P can cut it, and those two things alone makes it a big jump over the standard Type 054A.