I'd suggest adding an even more out-dated feel to them. Perhaps battle droids could be built on certain planets, while capturing Mon calamari could allow the production providence class ships from the quarren. As well replacing the tie compliments of each ship with an eclectic mix of droid fighters, skiprays, v-wings, and the existing v19 torrents would be cool.
Finally the alignment could be restricted from advanced imperial craft, like the ISD II, (but the tector could be used) and VSD mark IIs.
Keep in mind that while the Outer Rim in general did have a lot of older tech, the core of the Pentastar Alignment is the Braxant Sector and Velcar Free Commerce Zone, which were pretty rich, and the Alignment had the same access to most Imperial tech that any other group seemed to.
This doesn't belong here, but another suggestion is to make planets solely owned by a corporation able to make that unit for every faction. It make sense for a corporation to flip sides when there is a battle fleet and army threatening its assets. Kuat: the SD line, Rothana with it's walkers, Kamino with small numbers of clones.
This has come up a few times actually. Basically, the reason we don't do this is because we've seen several times in canon what happens when another faction does take over those planets, and it never results in those planets producing the same ships as they sued to for the new people controlling them. The New Republic took over Kuat and Fondor pretty early, and never produced ISDs or AT-ATs from KDY, nor showed any inclination to want to produce them. The senior design team also left Kuat for Byss when it happened, and when KDY produced ships for the NR, it was usually creating REC ships or with things like the Corona. The new owners almost always used the facilities to continue fabrication of the designs already existing within their military, or contracted them to create new designs. Even unique ship types like the Mon Cal Cruisers were made or fitted at other NR-controlled worlds to some extent, hence Thrawn being able to steal some from Sluis Van. The Imperials controlled Mon Calamari for years, and never produced militarized Mon Calamari Cruisers (especially considering the Mon Calamari only worked for them under extreme duress). Rendili was specifically given credit for the Republic-class Star Destroyer as a means to poilitically ingratiate them to the New Republic as opposed to continuing to make VSDs for the NR.