Since 7.5.4 was initially released there's been these updates:
What's new in Plesk v.7.5.4 build 75060118.21
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[*] hotfixes installation order issue fixed (cumulative psa-hotfix5 is created instead of all the previous hotfixes)
[-] phpBB site appication issue with wrong installation directory
[-] mchk memory leak issues
[-] several spamassassin bugs
[-] interface control hidding bugs
[-] rblsmtpd issue with inetd.conf
[-] PPWSE trigger issue with Sitebuilder upgrading
[+] Sitebuilder 2.1.2 is added
What's new in Plesk v.7.5.4 build 75051209.14
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[-] statistics security issue is fixed
What's new in Plesk v.7.5.4 build 75051115.01
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[+] New functionality is added to initial configuration page
What's new in Plesk v.7.5.4 build 75051017.14
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[-] Several PMM, API-RPC, CU bugs are fixed
[-] mchk bug with segmentation fault is fixed
[+] Sitebuilder 2.1.1 is added
[+] SBM 2.0 is added
What's new in Plesk v.7.5.4 build 75050928.18
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[-] Dr. Web starting causes qmail-queue to loose suid bit
[-] Sheduled Backups reset last timestamp
[-] Proftpd problem with group owner during file uploading
[-] Spam mail isn't deleted/marked
[-] Spamassassin corrupted by Watchdog
[-] Value for checkbox 'WWW-prefix' missed if domain administrator changes properties of the account
[-] Wrong permissions for /var/qmail/bin/qmail-queue after start/stop of Drweb
[-] Plesk does not recognize main IP
[*] Germany LP for watchdog is updated
[-] phpBB issue is fixed
What's new in Plesk v.7.5.4 build 75050915.19
==============================================
[-] 1. Fixed bugs in PMM with RaQ2 migration
[-] 2. Fixed bug in domain.sh CU with DNS zone management
[-] 3. Fixed bug in PMM with mail aliases migration
[-] 4. Fixed bug in cs-gs module with upgrade from 1.2.2 to 1.2.3
[-] 5. Fixed bug in HSPc: Plesk can't connect with MYSQL on VE created through HSPc
[+] 6. New plesk's component autoupdater is added
However, unless you are experiencing problems, I would advise against upgrading unless you are competent with SSH as it's very possible that things will break. If you go ahead and do it and things break ensure you're ready to react if you have any critical stuff on the server.