Whether or not to hire a lawyer for a first DWI is more of a financial decision than anything else. If you are a millionaire, you will almost certainly spend quite a bit of money on a defense team. There are excellent reasons to do so, and the lawyer will definitely help in the long run. If you are in a situation where you can get the money for a good DWI lawyer (say $3000-$5000), but it is not a trivial sum, you might be more inclined to do a cost/benefit analysis. What are you getting for your money? Let's talk about it, but first, a caveat.

This discussion is about a first-time DWI without any complications. If you have priors, someone was injured or killed as a result of your DWI, there were minors in the vehicle, or you received other serious charges like felony possession of a controlled substance, you need a lawyer. It is no longer a question of whether or not a lawyer is worth the money -  you need to protect yourself.

License Issues

The Missouri Department of Revenue (DOR) will try to suspend or revoke your license after you are arrested for a DWI. This is independent of the criminal charges the court will file. A lawyer can try to prevent this from happening by representing you at a hearing with the DOR. It is unlikely that a non-lawyer would have any success at one of these hearings. The only way to win is by clearly exposing technical mistakes made by law enforcement. 

To find one of these mistakes, you must collect all the police reports and videos related to your arrest. Then you need to know what type of mistake you are looking for. They are not always apparent; it can be a matter of a few words said or not said at the right time. 

Legal representation is even more critical when you refused to take a breathalyzer test. The DOR will revoke your license for one year with a refusal. A good DWI attorney can sometimes, even if they lose the hearing, negotiate a way for you to keep your license. 

Worst case scenario, if your lawyer loses the DOR hearing, they can walk you through the license reinstatement process. The DOR won't just hand you your license back after a DWI. There will be plenty of hoops to jump through, and an attorney can help make it easier. 

Negotiation

A DWI attorney can negotiate with the prosecutor to achieve a favorable outcome in your criminal case. You have every right to represent yourself, and you can try to deal with the prosecutor on your own, but it is hard to say if you will make any progress. Realistically, a vanishingly small number of people are likely to have any success at all. 

A skilled attorney can get surprisingly good results with negotiation. Sometimes, the charges are dismissed. More often, they are reduced to a lesser offense that avoids the impact of a DWI conviction. 

The key to a successful negotiation is finding flaws in the evidence that the state will use against you. The average person simply does not know how to accurately analyze the evidence in a DWI to find police errors. Many of the mistakes an office can make are errors of omission, meaning they failed to do something they were required to do. If you do not know all the steps an officer is supposed to make, it is hard to know which ones they missed. 

Trial

You should not represent yourself in a DWI trial. The judge will try to convince you to hire a lawyer, but if you choose not to, you will have a tough time representing yourself. Ideally, you should hire a lawyer well before your case reaches the trial stage. The good news is that you can hire an attorney at any time, and as long as the trial has not actually started, they can negotiate with the prosecutor. 

Guidance

Missouri DWI law is complicated. There will be many things you need to do to put the whole thing behind you, even in the best of circumstances. You might need to complete the Substance Abuse Traffic Offender Program (SATOP), the Mothers Against Drunk Driving Victim Impact Panel, get SR-22 insurance, put Ignition Interlock on your car, complete probation terms, etc. This is all second nature for an attorney who handles DWI cases, but it can be overwhelming if you are new to it. 

Hiring an experienced attorney with whom you have a good rapport can make this much more manageable. Many of these requirements are actually pretty simple if you know the right person to contact. A good DWI lawyer will have those contacts. You don't need to struggle through a DWI on your own.