Why don't witnesses get the same special balancing test? They don't: they get the regular Rule 403. And note that a witness's reputational interest isn't really considered-- we're only concerned about unfair prejudice to the party. You might arue that your client shouldn't be tarred with the same brush as the witness (since their crimes may well be similar), but that's not really the witness's interest.
Even misdemeanors are allowed if they involve falsity and dishonesty. And that appears to go for the accused as well. This is the crimen falsi issue. This is interesting: an awful lot of felonies have nothing to do with dishonesty. There's a matter of degree, and society's judgment that this is extreme conduct. But in the modern regulatory state, that hardly seems the case any more.
Now 609 is only for impeachment: we can only go after the accused under 609 if the accused is a witness.
Also note that 609 is just about the fact of a conviction, not the character for truthfulness (that would be 608). The WI rule about prior convictions (Wis. Stats. § 906.09; to convert a federal rule to a WI statute, put 90 in front of it and move the decimal point): you can ask "have you ever been convicted of a crime?" and then "how many times." WI doesn't let you name the crime, ask when it was, differentiate between felony and misdemeanors, etc. In Federal court, you can ask those questions, but you can also name the crime and the year.
In practical terms, judges will tend to exclude prior convictions, the older they are. 10 years is the federal standard. Now you don't just spring this on the judge, either: 104(a) the judge needs to make a ruling on the admissibility of this evidence out of the hearing of the jury. And at times, witnesses are instructed to give incorrect answers to juries, if certain convictions are ruled inadmissible (so: "how many times were you convicted" might really be "how many of your convictions should the jury hear about").
90 days later, an investigator interviews the witness, and the witness says "the white car had the red light."
At trial, the witness says the blue car. Opponent impeaches using the day 90 statements. We can use Rule 613, to introduce that prior inconsistent statement. On redirect, the proponent, obviously, wants to rehabilitate. So under Rule 801(d)(1)(b), we can get that statement from Day 1 in (prior consistent statement).
So you provide the witness with something in the hope that it jogs their memory. If that works, you take it away (it's not itself evidence), and then the witness can offer testimony from a now-refreshed recollection.
You can use anything to refresh memory: there are no restrictions (even a prompting from the lawyer).
You can gently impeach (prior inconsistent statement: Rule 613) under the guise of refreshing memory. So what may be rehabilitation with one witness may be a sort of impeachment with another.
How do you prove habit, if it's relevant in a lawsuit? You need prolonged or regular observations. So the length of time that a witness has known the person with the alleged habit, the kinds of observations made, corroboration by other people familiar with the person, etc. So you lay a foundation that someone would know about this habit, and you can use reputation evidence, and then you get testimony about it.