I don't think the issue is that straightforward. Comparing issues of the same bread and butter:
(1) Tan Kin Lian is of the establishment. To hear him speak does not carry any cost, except the transport fare.
Chee Soon Juan had been sued by the PAP leaders. Every Singaporean knows that it is dangerous to be associated with him. To hear him speak will carry a great deal of cost. You never know who is targetting and investigating you even if you shake his hands.
We will never know if such points are true. But people believed it is true. That is why JBJ standing in the MRT stations, mutely selling his books, had no takers. From the reactions to JBJ today, it is clear that many sympathized with him.
This is not to say that CSJ is the same as JBJ. Rather this is to say that once an opposition leader has been sued by the PAP leaders, singaporeans tend to shy away from them.
Tan Kin Lian has not been sued by the PAP leaders. If he has, then people will avoid him too.
(2) It is interesting that people relate those who speak at Speaker's Corner to be potential political party's candidates.
Thus will we see the emergence of a new political party in the near future?