The para-methyl substitution in related chemical classes appears to push the effects profile towards serotonin release (methcathinone to 4-mmc for example, although a better comparison might be ethcathinone to 4-mec since 4-me-TMP is definitely no mephedrone). Drawing comparisons like this is inherently speculative - the SAR may not translate at all. The serotonin release, if there at all, is probably a fairly weak effect. 4-Me-TMP is unusual in some other ways - the binding data doesn't fit well with the potency and its potency (as measured in rats) is far more variable than any other phenidate, which is good reason to suspect that there's more going on with it than the reuptake inhibition that was measured. Serotonin release is known to dampen perceived DRI effects, which would be consistent with the known data. Until someone does the necessary research, we're not going to know very much.
I really doubt you can apply the amphetamine/cathinone SAR here since Phenidates are basically pure reuptake inhibitors.
Neither Pyrovalerone (i.e. 4-Methyl-alpha-PVP) nor MDPV (which has a freaking Methylenedioxy bridge) are serotonin releasing agents, so it seems extremely unlikely that 4-Methyl-TMP would be either.
From what I understand, the general rule is that the more steric bulk you add to an amphetamine/cathinone, the more its profile shifts from releasing agent to reuptake inhibitor, so I see little reason to assume that an extra Methyl would add to MPH's already near-nonexistent monoamine releasing qualities.