I honestly think some of us are still struggling to align our expectations in the transfer market to where we currently find ourselves. Granted, we'll always be a big attraction in league one when compared against the rest of the clubs in the division, but we're still in league one all the same.
Putting Billy's previous spells to one side, he's a striker that has a good goal scoring ratio and has succeeded in this division before under the same manager. He's played plenty of football at the division above, granted with varied success, but in terms of 'proven' players, he's probably as proven as anyone we could expect to sign.
I'm also not sure what relevance his previous spells with us have. Different manager, different coaches, different team mates....his previous spells with us can't be used as an indicator as to how he will do this time.
Re: Sammon, I have to say I've only seen him a couple of times. Hopefully at league one level he will be more of a goal threat than he has been in divisions higher but he appears to be more of a foil to the main man at top rather than the man you expect to get the goals. Again, as a league one club, signing players that are capped at international level and have played a lot of football at a higher level shouldn't be sniffed at. Whether he is a success with us or not is another matter of course and time will tell, but I don't think the club or Adkins can be criticised for these signings.