Request a contested hearing and consult with a criminal defense attorney in private. There is no reason to simply pay the ticket. Many attorneys, including myself, offer free initial consultations.
Always fight every ticket! There is always a possibility you will win. The officer may come to court and forget his notes, he may not have the calibration for his radar, a million things can happen.
If you want to pay attorney fees to fight the ticket and possibly have the ticket not go on your driver's record then I would fight it. If you plan on fighting the ticket without the benefit of an attorney then your argument that you were not shown the radar reading when you requested to see it is not going to win your contested hearing. Often times there are other issues that you may not be able to know about unless you hire an attorney. If you can't afford an attorney and would like to get a guarantee that the ticket won't go on your record then I would see if you are eligible for a deferred finding. A deferred finding allows the infraction to not be reported to the Department of Licensing but you will still have to pay the fine for the infraction and agree to have no infractions for a period of time as set by the court. You can only use a deferred finding once every 7 years and may not be eligible in certain circumstances.
Given the speed you are accused of you should certainly request a contested hearing and try to get the ticket dismissed or reduced.
Since you were on I-90 in Roslyn I am assuming that your hearing will be in either the Upper or Lower division of the Kittitas County District Court, or at least somewhere in that area. Fighting tickets in Kittitas County can be difficult, so you should consult with an experienced attorney about your case.
In Washington, the officer is not required to show you the results off of the radar or laser "gun" that they used to determine your speed. Furthermore, you seem to admit that you were traveling 45-50 mph in a 35 mph zone. I understand that you could see the 50 mph sign, but you had not reached it yet. If a prosecuting attorney is present and you choose to fight the ticket yourself they could call you as a witness and you might actually end up hurting your case more than helping. If you hire an attorney you often do not need to attend the court hearing, and can avoid being a witness against yourself.
Many attorneys are available for a price similar to the fine on your ticket, and most will offer a free consultation. Feel free to give me a call if you have any questions - (206)724-2436.