Particle Lances are awesome and I really like them. In fact they might be slightly too good.
I'd say they're very strong, they
should be given the cost to obtain them, but they also have very clear weaknesses that are easy to exploit, which means they still require work and smart doctrine/tactics to use effectively (weak NPR tactical AI notwithstanding), so IMO they are in about the right place.
Particle beams are, IRL (according to the whitepapers regarding 60s-70s satellite design) spinals.
Mil SF (including derivatives such as various anime) have awesome scenes of gigantic spinal particle cannons.
Thus this suggestion: particle lances should take the spinal slot on warships on which they are mounted. This would mean you could only mount one (or two, if you have advanced spinals? I'm not clear these days on how spinal vs advanced spinal works, except giving you a larger aperture for lasers) and it would take 'the spinal slot' from other candidates. It would also require you to research spinal mounts before actually being able to mount a particle lance.
(Maybe advanced spinals still give you 1 damage/range tech above normal? I haven't thought that far in advance; this is based on Rule of Cool for me.)
The problem with spinal weapons in general is that they don't really scale well mechanically. Currently, If you have (say) 30 cm laser tech and Advanced Spinals, your biggest spinal weapon is a 45 cm laser which requires, IIRC, about 700 tons. That's a proper spinal weapon on a 5,000-10,000 ton ship, but not much more than a slightly bigger gun on a 50,000-ton dreadnought.
The natural solution seems to be scaling spinal weapons to be larger, but this poses a problem because the alpha strike from such weapons is difficult at best to balance in a way that preserves interesting gameplay and choices. For example, suppose a spinal weapon could be 3x the normal caliber, so with 30 cm laser tech a spinal laser could be 90 cm (1,400 tons, IIRC). This is not really such a great improvement in size, but more pressingly a 90 cm spinal laser has over 200 base damage compared to 24 for a 30 cm laser (not to mention >2x as large of a range modifier, so that damage holds up at a much longer range). That's a really big alpha hit that can probably wipe out many ships in one shot, especially those without shields, which means you wind up with a meta where spinal lasers are THE beam weapon - even making spinal weapons larger and less efficient than their corresponding normal weapons of the same caliber doesn't solve this, unless it makes spinals basically useless. This is the root of the problem: if you add a weapon that is as powerful as these massive weapons we see in science fiction settings, it creates tremendous difficulties to balance and the result is almost certainly an unstable equilibrium at best.
(It's worth noting that the current situation hails from the VB6 days when, for a long time, most players were designing smaller ships on which a Spinal Laser actually lived up to its billing. Changes in the C# versions as well as the player base learning better strategies over time has led to larger ships becoming more common if not the normal approach for many players. In this sense, spinal weapons are a bit of a historical artifact.)
IMO, massive dreadnought-scale spinal weapons fall under the same umbrella as tiny space superiority fighters - very common in science fiction, but not really a good fit for Aurora's mechanics. That being said, I do enjoy the niche they currently have, as charging with a wing of spinal-armed FACs/LACs is a very fun doctrine.
