I typically don't buy shards from the Shard Shop unless it's Vader. However, there have, on occasion, been other characters (such as Jawa Engineer) that I would've liked to purchase shards for.
Yes, Jawa Engineer did show up for me occasionally in the shard shop. The problem is, he showed up very infrequently and only offered 2 shards at a time. This means that if I would have purchased his shards, I would've needed him to appear a minimum of 3 times before I would actually have been able to purchase enough shards to reduce the amount of time it took me to farm him, and he would have needed to appear 5 times to prevent me from wasting some of the shards. Given how infrequently he appears in the Shard Shop (along with every other character), it simply seemed like too much of a gamble for me to think it was worth investing in spending shard shop shards on him.
This is because Jawa Engineer only shows up in bundles of 5 in the guild rewards, but shows up in bundles of 2 in the Shard Shop. If I knew that when I purchased shards of a character other than Vader in the Shard Shop it would be guaranteed to reduce my farming time, I might be a lot more likely to purchase their shards that way. But, as it is, purchasing shards for a character like this only 2 at a time doesn't really make sense.
My suggestion is for characters that are only available 5 at a time (such as Jawa Engineer, Gamorrean Guard, Chief Nebit, etc.), they should only appear in bundles of 5 in the Shard Shop. Other characters (such as Luke, Royal Guard, etc.) that can be obtained one at a time should continue to be available in bundles of 2.
Also, I'm not talking about changing the rate of Shard Shop shards to character shards. I know a lot of people have complained about the low number of character shards offered in exchange for their shard shop shards, but that's not the purpose of this suggestion. As far as I'm concerned, if 2 character shards cost 300 Shard Shop shards, I'm fine with 5 character shards costing 750 Shard Shop shards, or whatever rate the devs determine is appropriate.
Also, it's worth pointing out if this change does actually get made that most people currently don't keep a lot of Shard Shop shards on-hand, and therefore it might take a little while before anyone sees an increase in the number of character shards purchased from the shard shop. I know that I currently only keep roughly 1,000 Shard Shop shards on-hand maximum right now (so I can get Vader if he shows up), but if I knew that good characters that I want to farm were going to appear in bundles of 5, I might actually start keeping more shard shop shards on-hand, but it also might take a few days for me to build them up.