Slacker, why come back and forth Msia and Spore?

Once u got the SPR, u r SPR permanently.  You could live in Spore permanently. 
Re-entry permit, as uggested by the name, is to allow re-enter to Spore from overseas as Sporean i.e. no embarkation form needed, and via Spore citizen lane at their checkpoint.
To obtain/renew re-entry permit, one of the criteria is u need to "contribute" to Spore.  Thus u need to have a job.  Employer letter/cpf acct statement/income tax eval form are few of the required docs for the application/renewal.  Usually if u are at work for > a year with >2k mthly salary, u shall be able to get the renew of another 5 years. 
For your case, if u could get a job before Nov, u'll still stand chance to get the re- entry permit renewal for shorter period, maybe 1 year.
Another way, if u r a lady, go married to Spore guy and get dependent pass and u would have re-entry permit too.

Here is the tricky part. 
SPR allows u to live in Spore permanently provided u stay in Spore forever, no stepping out of the boundary.
Without re-entry permit, once u stepped out of Spore, when wanna go back to Spore, u'll lose the privillege.  U'll be treated as other normal foreigners...gotta fill up embarkation, only allows 2 weeks stay bla bla bla.       
Conclusion, SPR is just nothing.  Unless u wanna "jail" in the little island, otherwise to secure the rentry permit to have movement freedom is more important.

Where I got this info?  Check ICA.
http://app.ica.gov.sg/index.asp