The 350/600/2500 seems like pretty good milestones to me as well.
One area that I think would get undervalued in the stat lines, but is a key part of many teams is the setup men. In ML baseball, your top relievers are generally speaking all closers. There are a few top setup men who can collect a "Holds" stat, which isn't offered in HD, but most top setup men eventually slide into the closer role, rightly or wrongly. Conversly in HD, many shy away from listing a closer, and want their top setup men in there for the 7th or 8th inning, if caled upon. W/o the hold stat, they'll typically fall short of an impressive wins stat as well as an impressive save stat.
I also wish there were playoff stats listed on the main page, actually a lot more stats in general, but especially playoff stats and how they compared over their "prime years" to other players at their position. There's a pitcher in one of my worlds which has been solid for the most part in the regular season. He was already a major leaguer (27 I think) when the world was created, and is now 37. He's collected roughly 115 wins, despite playing on some poor teams the last 3 seasons as he started to age. However, in the postseason, he's like 15-2. He lead 3 teams to 4 different WS championships, including an impressing 4-1 w/ like a 1.5 for his first ring, and a 6-0 mark for his last ring. The World Chat and HoF chat are good places to pimp a guy like that, but the stats listed, which is all some will look at won't tell the whole story.
How much do others consider the value of individual awards and team awards. Do WS rings boost a guy a little higher than he would otherwise be? Does a guy "need" an MVP award to make the hall, or a pair of silver sluggers? How many gold gloves would it take for one to give a player their "ozzie smith" award?
FWIW, one of the developers in one of my world said they are close to making the vote counts avialble right after the HoF announcements, rather than having to wait until the following voting period.